The fishing town of Gallowmere has been dying. For three months, the catch has dwindled to nothing. Fishermen who venture too far don't return. The sea itself seems wrong,oily, thick, and at night it hums with a sound that makes people's teeth ache. Livestock birth malformed young. Children draw pictures of "the thing with many mouths" in their sleep.
The party arrives as hired swords, summoned by the town's last surviving council member, a half-blind woman named Miriam Salt. Her message was simple: "Something is eating us from below. Find it. Kill it. Or we're all dead by winter."
What awaits them is an descent into an eldritch nightmare,a thessalhydra, ancient and terrible, awakening beneath the cliffs. But the hydra is merely the apex of a corrupted ecosystem, and the party must fight through its servants, its spawn, and the very land itself to reach the beast's lair.
ACT I: THE ROTTING SHORE (Hours 1-3)
Opening: Gallowmere (30 minutes)
The party arrives at dusk. Gallowmere is a skeleton of what it was,boarded windows, empty docks, the stench of rotting fish. Only about 40 souls remain of the original 200.
Miriam Salt (elderly human, weathered, one milky eye) greets them at the Saltbone Inn. She's blunt:
Fishermen vanished. Boats found shredded.
The lighthouse at Widow's Point went dark two weeks ago. Keeper Aldous hasn't been seen since.
There's a sound at night from the cliffs. Like singing, but wrong.
She'll pay 500gp each if they can end this. She has nothing else to offer.
Roleplay opportunity: The innkeeper, Greaves (nervous, twitchy), mentions his daughter drew "eight moons with teeth" before she died of fever last week. A drunk fisherman, Old Cray, mutters about "the Deep Hymn" and how "it calls the faithful down."
Night Event: As the party rests, they hear it,a low, resonant thrumming from beneath the earth. It's almost musical, but it makes their bones vibrate uncomfortably. Constitution saving throw (DC 12) or be unable to sleep well (disadvantage on first check tomorrow). The druid might recognize this as deeply unnatural,no animal or natural phenomenon makes this sound.
The Widow's Point Lighthouse (1.5 hours)
A mile up the coastal cliffs. The lighthouse is dark, door ajar. Blood trails lead inside.
Exterior: Tide pools around the base are filled with dead crabs, all facing the same direction,toward the sea. Survival check (DC 13) reveals webbed, clawed tracks leading from the water to the lighthouse.
Interior - Ground Floor: The main chamber reeks of brine and rot. Furniture is overturned. Claw marks on the walls. A journal lies open:
"Day 40: The hymn grows louder. I see them in the water now,pale shapes, swimming in circles. They're waiting. Day 43: Aldous has stopped eating. He sits by the window, watching. He says 'Mother calls.' Day 44: I hear scratching at the door. Aldous is gone. I've barricaded myself upstairs. If anyone reads this,don't go into the water. Don't listen to the,"
The entry ends in a smear of blood.
Encounter 1: The Drowned Ones (CR 4 total)
3 Drowned Cultists (use Sea Spawn stats: AC 11, HP 32 each, +4 to hit, 1d6+2 bludgeoning + 1d6 poison)
These are Aldous and two fishermen, transformed. Pale, bloated, with gills and webbed claws. They attack on sight, gurgling "Mother... feeds... us..."
Tactics: They try to grapple and drag victims toward windows/water. The rogue can pick them off from range; the barbarian can break grapples; the paladin's radiant damage causes them to shriek.
Loot: Aldous wears a silver lighthouse keeper's medallion (worth 50gp, but radiates faint abjuration magic,can be used as a component for protection from evil/good).
Upper Lighthouse: The lamp chamber is shattered. At the center is a makeshift altar,bones arranged in a spiral pattern, all facing a crude carving of something with many heads.
Investigation (DC 14): The bones are recent. Human. Arranged in a pattern that resembles tidal charts.
Religion (DC 13): This is a summoning circle, but degraded. Whatever was called didn't need much convincing,it was already close.
Religion (DC 16): The symbol matches ancient texts about the Drowned Gods,primordial horrors that predate modern deities.
Nature (DC 15 - Druid advantage): The bones show signs of rapid mutation before death,extra joints, gill formations, scale growth. This isn't a disease. It's a transformation.
First Godly Weapon - The Paladin's Gift:
Hidden beneath the altar bones is a locked iron coffer (Rogue can pick, DC 15, or it can be smashed open AC 19, HP 15).
Inside: Tidebreaker, a longsword with a blade that seems to shimmer like sunlight through water. The crossguard is shaped like breaking waves.
Tidebreaker (Longsword, requires attunement by a paladin)
+2 weapon
Deals an extra 1d8 radiant damage to aberrations and undead
Once per day, the wielder can cast Crusader's Mantle (no concentration required, lasts 1 minute)
The blade sheds bright light in a 10-foot radius and dim light for another 10 feet. This light is sunlight.
The blade feels right in the paladin's hands, warm and steady. A voice,not quite sound, more like a memory,whispers: "Stand against the deep."
The Cliff Descent (30 minutes)
From the lighthouse, the party can see it: a massive cave entrance at the waterline, only accessible at low tide. The thrumming sound emanates from within.
Skill Challenge: Getting down the 200-foot cliff safely.
Athletics/Acrobatics to climb (DC 13)
Rogue can scout ahead, set pitons (advantage for others)
Druid can use spider climb or wild shape to help
Failure by 5+: fall 2d6 x 10 feet (grab a ledge halfway with Dex save DC 14)
At the bottom, the tide pools are filled with pieces,chunks of whale blubber, shark teeth the size of daggers, fish heads with too many eyes.
Cave Entrance: Wide enough for three people abreast. The walls glisten with a phosphorescent slime (harmless, but eerie,casts green-blue light). The thrumming is louder here, almost rhythmic.
ACT II: THE FLOODED HALLS (Hours 3-6)
The Sunken Temple (1 hour)
The cave opens into a vast, partially flooded chamber,clearly not natural. Crumbling pillars carved with maritime scenes (ships, krakens, drowning sailors) hold up a ceiling 40 feet high. The water is 3 feet deep, murky, and warm.
History (DC 14): This is pre-human. Sahuagin? No,older. The architecture predates known civilization.
Arcana (DC 15): The carvings aren't decorative. They're instructional,depicting a ritual to "call the Mother of Depths."
Perception (DC 13): Something large moves beneath the water. Multiple somethings.
Encounter 2: Hydra Spawn (CR 6 total)
2 Hydra Spawn (custom): AC 14, HP 67 each, +6 to hit, 1d8+4 piercing damage
Two-Headed: Each spawn has two heads. Advantage on Perception checks and against being blinded, charmed, deafened, frightened, stunned, or knocked unconscious.
Reactive Heads: When the spawn takes damage, one head can make an opportunity attack.
Acidic Blood: When the spawn takes piercing or slashing damage, it sprays acid in a 5-foot radius (Dex save DC 13, 2d6 acid damage, half on success).
Tactics: They emerge from the water, serpentine bodies coiling. They try to separate the party, using the pillars as cover. The warm water is difficult terrain. The rogue can use pillars for advantage; the druid might control water or wild shape into something amphibious; barbarian rage resists the acid; paladin's radiant damage cauterizes, preventing the acid spray.
Loot: Among the bones at the bottom: 200gp in old coins, a pearl of power, and a waterlogged spellbook containing control water and water breathing.
LEVEL UP TO 6
The Breeding Pits (1.5 hours)
Beyond the temple, the tunnel slopes downward. The water deepens to 4 feet, then 5. The thrumming is now accompanied by wet, slithering sounds.
The passage opens into a nightmarish cavern: dozens of fleshy sacs attached to the walls and ceiling, each the size of a horse. They pulse rhythmically. Inside, shadowy shapes twist.
Nature/Medicine (DC 14): These are eggs. Gestation sacs. Whatever's inside is nearly ready to hatch.
Arcana (DC 13): The magic here is overwhelming,transmutation and conjuration, twisted together. This place is a factory of corruption.
At the center of the chamber, tending the sacs, is The Shepherd,a hulking sahuagin corrupted beyond recognition. Its body is covered in additional mouths that whisper in Aquan: "Mother feeds us. Mother loves us. We are her children."
Encounter 3: The Shepherd (CR 6)
The Shepherd (modified Sahuagin Baron): AC 16, HP 97, +7 to hit, 2d6+4 piercing + 1d6 necrotic
Multiattack: Three attacks - bite and two claws
Additional Mouths: As a bonus action, all mouths scream. All creatures within 20 feet must make a Wisdom save (DC 14) or be frightened until the end of their next turn.
Blood Frenzy: Advantage on attacks against wounded creatures
Regeneration: Regains 10 HP at the start of its turn if it has at least 1 HP
Add:
4 Sahuagin (AC 12, HP 22 each, +3 to hit, 1d6+1 piercing): They emerge from the water to defend the Shepherd
Tactics: The Shepherd fights defensively, using the sahuagin as shields while trying to frighten the party. It retreats toward the eggs if bloodied, trying to rupture them to release premature spawn (if an egg is destroyed, a malformed hydra spawn emerges but only has 30 HP and one head).
Second Godly Weapon - The Druid's Gift:
After the battle, one of the egg sacs pulses differently,greener, with vines growing through it. It's been corrupted differently, nature trying to fight back.
Inside: Rootcaller, a quarterstaff of living wood that blooms with tiny white flowers.
Rootcaller (Quarterstaff, requires attunement by a druid)
+2 weapon
When you cast a spell of 1st level or higher that restores hit points, all creatures healed regain an additional 1d6 hit points
You can use your Wild Shape as a bonus action instead of an action
Once per day, you can cast Plant Growth (the enrichment version takes 1 action instead of 8 hours)
The staff can be used as a druidic focus
The wood thrums with life, warm and vital against the corruption surrounding it. The druid can feel the ancient forests speaking through it: "Life endures."
The Drowned Gallery (1 hour)
A long, descending tunnel. The water is now chest-deep (difficult terrain for non-aquatic movement). The walls are covered in carvings,an entire history:
Ancient humans worshipping something in the deep
Ships bringing sacrifices
A great binding ritual, sealing something away
The bindings cracking
Recent: crude additions showing the thessalhydra's awakening
History (DC 16): This is the Covenant of Chains,a thousand years ago, a circle of druids and clerics bound the thessalhydra here, using the natural rock and blessed anchors. But the bindings have failed.
Investigation (DC 14): The recent carvings are... worshipful. Someone has been coming down here, celebrating the hydra's return.
Ahead, candlelight flickers.
Encounter 4: The Cult (CR 7 total)
A chamber opens up, dry, with a raised platform. Here, High Cultist Maren (human woman, eyes replaced with black pearls) leads a group in prayer.
High Cultist Maren (use Priest stats with modifications): AC 13 (dark robes), HP 52, +5 to hit (spear), 1d6+2 piercing
Spellcasting (5th level):Command, hold person, spirit guardians (appears as drowning hands), guardian of faith (appears as a pillar of water)
Blessing of the Deep: Allies within 30 feet have advantage on saves against being frightened and gain 10 temporary HP when she casts a spell
6 Cultists (AC 10, HP 9 each, +3 to hit, 1d4+1 slashing with daggers)
Fanatic Devotion: When reduced to 0 HP, they use their reaction to make one final attack
Tactics: Maren casts spirit guardians immediately (the drowning hands create difficult terrain and deal 3d8 damage). She uses hold person on martial characters while cultists swarm the held targets. The cultists fight to the death, screaming hymns.
Roleplay opportunity: If Maren is captured/questioned:
She's ecstatic, not afraid: "Mother is awake! The Hymn has called us!"
She came to Gallowmere specifically to help the awakening: "We prepared the way,blood in the water, prayers in the dark."
The thessalhydra promised transformation: "We will be remade, perfected, no longer weak flesh but HER children."
She knows the way deeper: "Through the Feeding Chambers, past the Anchors. She waits. She hungers."
Loot:
Maren's black pearl eyes (500gp each, but radiate evil,Paladin detect evil reveals they're cursed)
A map carved on sharkskin showing the route to the thessalhydra's lair
Ring of water walking
6 doses of potions of healing
LEVEL UP TO 7
ACT III: THE FEEDING DEEP (Hours 6-9)
The Anchor Chambers (1.5 hours)
Following the map, the party reaches a series of three chambers, each containing one of the ancient anchors used to bind the thessalhydra. Each is a massive stone pillar carved with divine symbols, glowing faintly with failing magic.
The water here is deep,10 feet in most places, requiring swimming (the ring of water walking helps, as does water breathing if the party prepared it).
Each chamber has a guardian,remnants of the binding ritual, now corrupted:
Chamber 1: The Chained Druid
Corrupted Treant (the petrified druid from the original binding has awakened, roots fused with the anchor): AC 16, HP 138, +10 to hit, 3d6+6 bludgeoning
Animate Trees: Can animate 2 pieces of driftwood (use Awakened Tree stats, HP 59 each)
Corrupted: Instead of fire vulnerability, has necrotic resistance
Root Prison: One target, Strength save DC 15 or be restrained by roots (2d6 piercing per turn, can break free with DC 15 Strength check)
The druid's face is visible in the trunk, screaming silently. If the party destroys the anchor after defeating the treant, the druid's spirit is released and whispers a warning: "Eight heads. Eight hungers. It cannot die while even one feeds."
Chamber 2: The Blessed Sentinel
Corrupted Guardian Naga: AC 18, HP 127, +8 to hit, 1d8+4 piercing + 3d8 poison (Constitution save DC 15 half poison)
Rejuvenation: If killed, reforms in 1d6 days (unless the anchor is destroyed)
Aquatic: Swim speed 40 ft, can breathe underwater
The naga was once a guardian of the binding. Now it serves the hydra. It fights intelligently, using counterspell against healing and blight against the druid.
Chamber 3: The Drowned Knight
Revenant Knight (the champion who led the original binding): AC 17 (half-plate + shield), HP 136, +7 to hit, 2d8+3 slashing
Multiattack: Two attacks
Vengeful Tracker: Advantage on attacks against whoever damaged it most recently
Turn Immunity: Immune to being turned
Regeneration: Regains 10 HP at start of turn if it has at least 1 HP
This was once a hero. Now its armor is rusted, face skeletal, eyes burning with cold fire. It doesn't speak, just attacks with mechanical precision.
Third Godly Weapon - The Barbarian's Gift:
When the knight falls, its armor crumbles to rust. But its weapon remains: Stormbreaker, a greataxe crackling with primal fury.
Stormbreaker (Greataxe, requires attunement by a barbarian)
+2 weapon
While raging, you deal an extra 1d10 lightning damage on hit
Critical hits with this weapon deal maximum damage instead of rolling
Once per day while raging, you can call down a lightning bolt (as the spell, save DC 15, 8d6 lightning damage) that doesn't harm you
You have resistance to lightning damage while attuned
The axe feels like a thunderstorm contained in steel. When the barbarian grips it during rage, lightning arcs between their fingers. It roars for battle.
The Feeding Grounds (45 minutes)
With the anchors destroyed, the way to the thessalhydra's lair is open. A massive tunnel, 30 feet wide, slopes down into darkness. The thrumming is now deafening,a physical pressure against the ears.
The water rushes downward, creating a current. The party must navigate carefully (Athletics checks DC 13 or be swept along, taking 2d6 bludgeoning from impacts).
The tunnel opens into a vast cavern,the Feeding Grounds. Here, the thessalhydra has dragged its kills. The floor is a charnel pit: whale bones, ship wreckage, human remains by the hundreds. The water is thick with blood.
Perception (DC 12): Movement in the bones. Something large.
Encounter 5: The Bonecrusher (CR 8)
Young Remorhaz (corrupted by proximity to the hydra): AC 14, HP 142, +11 to hit, 3d10+5 piercing + 3d6 fire
Heated Body: Creatures that touch it or hit with melee attack within 5 feet take 3d6 fire damage
Swallow: One Large or smaller creature, Dexterity save DC 15. Swallowed creature is blinded/restrained, has total cover, takes 3d6 acid + 3d6 fire per turn. If the remorhaz takes 30+ damage in one turn from inside, it must succeed on a DC 21 Constitution save or regurgitate the creature.
Burrowing: Can move through bone and rubble, leaving a tunnel
This creature has been feeding on the hydra's scraps, growing massive. It erupts from beneath the bones, superheated from the hydra's proximity.
Tactics: It tries to swallow the highest-damage dealer (likely the barbarian), then burrow away to digest. The rogue can attack from range; the paladin and druid must avoid the heated body while dealing damage. If it swallows someone, the party must decide whether to focus fire or try to force regurgitation.
Fourth Godly Weapon - The Rogue's Gift:
Among the treasures in the bone pile:
2,000gp in assorted coins and jewelry
A wand of fireballs (3 charges)
Shadowfang, a pair of elegant daggers that seem to drink in light
Shadowfang (Pair of daggers, requires attunement by a rogue)
+2 weapons
When you hit with these daggers using Sneak Attack, add an extra 2d6 necrotic damage
Once per turn when you hit a creature with one dagger, you can teleport up to 30 feet to an unoccupied space you can see, and you can make one attack with the second dagger as part of the same action
You can see normally in magical and non-magical darkness up to 120 feet while holding at least one of these daggers
You have advantage on Dexterity (Stealth) checks while holding both daggers
The daggers feel weightless, extensions of shadow. When the rogue holds them, they seem to blur at the edges, as if not entirely present in this reality.
ACT IV: THE MOTHER OF DEPTHS (Hours 9-10)
The Thessalhydra's Lair (1 hour, 15 minutes)
Beyond the Feeding Grounds, a massive archway,clearly artificial, carved with warnings in a dozen dead languages. All say variations of: "SEALED BY COVENANT. DO NOT BREAK THE CHAINS. THE MOTHER MUST NOT WAKE."
The archway leads to a cathedral-sized cavern. The ceiling is lost in darkness above. A vast pool dominates the center, 50 feet across, water black as ink. Around the pool's edge: the broken remains of the three anchors, their chains snapped.
The thrumming stops.
Silence.
Then: "You... come... to... feed... Mother?"
The voice comes from everywhere and nowhere,eight voices speaking in unison, overlapping, creating a nauseating harmony.
The thessalhydra rises.
FINAL ENCOUNTER: The Thessalhydra (CR 11)
Thessalhydra (Legendary)
AC 16 (natural armor)
HP 280 (main body)
Speed: 30 ft., swim 50 ft.
Legendary Resistance (3/day)
Abilities:
STR +6, DEX +2, CON +7, INT -2, WIS +3, CHA +1
Senses: Darkvision 120 ft., passive Perception 13
Languages: Understands Aquan and Deep Speech but speaks in overlapping echoes
Special Traits:
Eight Heads: The thessalhydra has eight heads. While it has more than one head, the thessalhydra has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.
Whenever the thessalhydra takes 30 or more damage in a single turn from a single source, one of its heads dies. If all its heads die, the thessalhydra dies.
At the end of its turn, it grows two heads for each head that died since its last turn, unless it has taken radiant damage since its last turn. The thessalhydra regains 15 hit points for each head regrown this way. (Maximum 12 heads total)
Multiple Heads: The thessalhydra can take one reaction per head.
Reactive Heads: For each head beyond one, the thessalhydra gets an extra reaction that can be used only for opportunity attacks.
Wakeful: While the thessalhydra sleeps, at least one of its heads is awake.
Aquatic Advantage: The thessalhydra has advantage on attack rolls while both it and its target are in water.
Psychic Hymn (Aura): At the start of each of the thessalhydra's turns, all creatures within 30 feet must succeed on a DC 16 Wisdom saving throw or take 2d6 psychic damage and have disadvantage on attack rolls until the start of the thessalhydra's next turn.
Actions:
Multiattack: The thessalhydra makes as many bite attacks as it has heads (starting with 8).
Bite: Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 1d10+6 piercing damage.
Acid Spray (Recharge 5-6): The thessalhydra sprays acid in a 30-foot cone from one of its heads. Each creature in that area must make a DC 16 Dexterity saving throw, taking 6d6 acid damage on a failed save, or half as much on a successful one.
Grasping Tentacles (Recharge 6): Four tentacles erupt from the thessalhydra's body. Each tentacle attacks one creature within 20 feet (+10 to hit, 2d6+6 bludgeoning damage, target is grappled, escape DC 16). While grappled, the target takes 2d6 bludgeoning damage at the start of each of its turns. The thessalhydra can grapple up to four creatures this way.
Legendary Actions (3 per round):
Detect: The thessalhydra makes a Wisdom (Perception) check.
Bite Attack: The thessalhydra makes one bite attack.
Thrashing Coils (Costs 2 Actions): The thessalhydra thrashes its massive body. Each creature within 10 feet must succeed on a DC 16 Strength saving throw or take 3d8 bludgeoning damage and be knocked prone.
Submerge and Strike (Costs 3 Actions): The thessalhydra submerges into the pool (if in water) or slithers to a new position (if on land), moving up to its speed without provoking opportunity attacks, then makes a bite attack with advantage.
The Battle:
Phase 1 (HP 280-200): The thessalhydra fights cautiously, using its reach and multiple attacks. It focuses on spreading damage across the party, testing their defenses. Uses legendary actions for bite attacks primarily.
Phase 2 (HP 199-100): The thessalhydra becomes aggressive. Starts using Acid Spray whenever available. Uses Grasping Tentacles to isolate targets (tries to grapple casters/ranged attackers and drag them into the water). Heads begin to die and regrow,unless the party uses radiant damage (Paladin's Tidebreaker or spells).
Phase 3 (HP 99-0): Desperate and enraged. The thessalhydra uses Thrashing Coils frequently (costs 2 legendary actions). If reduced below 50 HP, it tries to swallow a character whole (use modified swallow: one head can attempt to swallow one Medium or smaller creature that is grappled by tentacles,Strength save DC 16 or be swallowed. Swallowed creature takes 4d6 acid per turn and grants the thessalhydra +2 AC as a "shield").
Environmental Hazards:
The pool is 30 feet deep. Creatures in the water when the thessalhydra submerges must make a DC 14 Strength save or be pulled 10 feet toward it.
The cavern walls are unstable. When the thessalhydra uses Thrashing Coils, rubble falls from above. All creatures must make a DC 13 Dexterity save or take 2d6 bludgeoning from falling rocks.
The Psychic Hymn aura makes concentration difficult and punishes clustering.
Tactical Considerations for the Party:
Paladin:Tidebreaker's radiant damage prevents head regeneration,crucial. Crusader's Mantle gives everyone +1d4 radiant damage. The light helps with visibility.
Druid:Rootcaller lets them shift forms as a bonus action to adapt (Water Elemental form to fight in the pool, Earth Elemental for resistance). Healing is essential. Control water can manipulate the pool.
Barbarian:Stormbreaker's critical hits can take out heads quickly. Rage resists the physical damage. The lightning bolt can hit multiple heads.
Rogue:Shadowfang's teleport allows repositioning to avoid grapples and AoE. Sneak attack + extra necrotic damage on isolated heads. Darkvision helps if lights go out.
The key: recognize that radiant damage stops regeneration. Cut off heads faster than they grow back. Manage the grapples (the bound character or an ally must break free). Survive the psychic aura (spread out or use calm emotions if available).
Victory and Aftermath (15 minutes)
When the thessalhydra finally dies, its body dissolves into black ichor that evaporates with a sound like screaming. The psychic hymn stops,the sudden silence is almost painful.
The cavern begins to collapse,the thessalhydra's presence was holding the structure together.
Skill Challenge: Escape
5 successes before 3 failures
DC 15 Athletics/Acrobatics to navigate collapsing tunnels
DC 13 Perception to spot safe paths
DC 14 Survival to remember the route back
Druid can wild shape to carry injured, stabilize the path with plant growth or stone shape
Barbarian can hold up falling rocks for others to pass
Rogue can find shortcuts
Paladin can use Tidebreaker's light to illuminate the way
Success: They emerge from the lighthouse cave as the cliffside collapses into the sea. The thrumming is gone. The water is clear.
Failure: They escape but take 4d10 bludgeoning damage from cave-ins and near drowning.
Epilogue:
The party returns to Gallowmere at dawn. The sun is rising,something the townspeople haven't seen clearly in months.
Miriam Salt greets them, tears in her good eye. The fish have returned to the nets. Children slept peacefully last night for the first time in weeks.
Rewards:
500gp each as promised
The town throws a feast (humble but heartfelt)
Miriam gifts them her family's heirloom: a cloak of the manta ray
The lighthouse keeper's guild sends a reward: 1,000gp and a +1 shield emblazoned with a lighthouse beacon
I'd say you've got a great adventure frame here. I have two things I'd point out though.
1 - This is a pretty 'on rails' adventure. It is very linear. That's not necessarily a bad thing, but are preparing too for player characters to try unusual courses of action? If no, I'd suggest trying to consider some other options. What for example if the party decide simply to collapse the cave entrance, deciding that 'hey this is the best way of sealing the dangers within'?
2 - What is the motivation for the party? Is there an imminent danger to the characters? Is the final boss really that much of a risk? The stakes here don't really seem to provide a motivation for the player characters beyond them being heroes and wanting to do 'good deeds'. I've had player characters in the past who would look at the potential dangers, shrug and simply set up a town hall meeting to convince the civilians to abandon their homes and leave this tainted place.
To be clear, there's a lot of good thought here, and some parties LOVE a linear experience. I have some players who just cannot deal with an open world and infinite choices. I've got other players who need to know they've got the options to do whatever chaotic thing pops into their mind. It'll depend on the table, but I'd say you've got a great outline for a solid adventure.
1) It is a wonderful outline. Just remember that your players won't necessarily do as you expect.
2) As far as I can tell, they are level 7 for the final encounter since there are no level ups listed past Act III. You're thinking appears to be that the Paladin would have Crusader's Mantle as a prepared spell and would have both the spell slot and the spell available for the final encounter.
- Paladin's don't get 3rd level spells until 9th level.
- Crusader's Mantle is a 3rd level spell and the character will have at most 2 third level slots.
- the encounter plan does not seem to have a long rest between Act III and Act IV so the characters would likely be down both hit points and spell slots coming into the final encounter - likely making your ideas of how the party might deal with the encounter invalid.
The paladin has 2 attacks - radiant damage prevents regeneration but what happens if the paladin misses? What happens if the hydra hits the paladin and they lose concentration on Crusader's mantle. The hydra gets one attack/head starting with 8! Assuming it is an intelligent creature, why would it choose to spread attacks around and not try to take down a character as quickly as possible (other than the fact it isn't fun for the player?).
3) You mention the druid turning in to elementals. This assumes you are playing the 2014 version of 5e AND that the druid is at least a level 10 moon druid - which can already shape shift as a bonus action ... the option isn't available before then. The rootcaller description doesn't seem to give the druid additional wildshapes. Using the 2024 rules, shifting into an elemental isn't an option. So, I am not sure what you are thinking here unless a bunch of house rules are involved.
4) Killing a head requires 30 or more damage on a single turn from a SINGLE source. The only martial builds (paladin, rogue or barbarian) that I've seen that might be able to do that are 2014 Great Weapon Master and Sharpshooter builds and even then they would rarely hit 30 damage from a single attack. On the other hand, perhaps you mean total damage from an individual character - this is more doable but still challenging.
Anyway, the hydra encounter seems to me like a possible recipe for a TPK given the outline for the adventure.
P.S. 8 attacks at +10 doing d10+6 ... will add up quite quickly. For a 20 AC character - about 50% will hit every turn doing an average 46 damage - which is probably almost enough to take out some level 7 characters. Level 7 rogue with 12 con would be 45.
2) As far as I can tell, they are level 7 for the final encounter since there are no level ups listed past Act III. You're thinking appears to be that the Paladin would have Crusader's Mantle as a prepared spell and would have both the spell slot and the spell available for the final encounter.
- Paladin's don't get 3rd level spells until 9th level.
- Crusader's Mantle is a 3rd level spell and the character will have at most 2 third level slots.
What happens if the hydra hits the paladin and they lose concentration on Crusader's mantle.
Tidebreaker gives free crusaders mantle no concentration required.
“Mother of Depths” - Start at Level 5
OVERVIEW
The fishing town of Gallowmere has been dying. For three months, the catch has dwindled to nothing. Fishermen who venture too far don't return. The sea itself seems wrong,oily, thick, and at night it hums with a sound that makes people's teeth ache. Livestock birth malformed young. Children draw pictures of "the thing with many mouths" in their sleep.
The party arrives as hired swords, summoned by the town's last surviving council member, a half-blind woman named Miriam Salt. Her message was simple: "Something is eating us from below. Find it. Kill it. Or we're all dead by winter."
What awaits them is an descent into an eldritch nightmare,a thessalhydra, ancient and terrible, awakening beneath the cliffs. But the hydra is merely the apex of a corrupted ecosystem, and the party must fight through its servants, its spawn, and the very land itself to reach the beast's lair.
ACT I: THE ROTTING SHORE (Hours 1-3)
Opening: Gallowmere (30 minutes)
The party arrives at dusk. Gallowmere is a skeleton of what it was,boarded windows, empty docks, the stench of rotting fish. Only about 40 souls remain of the original 200.
Miriam Salt (elderly human, weathered, one milky eye) greets them at the Saltbone Inn. She's blunt:
Roleplay opportunity: The innkeeper, Greaves (nervous, twitchy), mentions his daughter drew "eight moons with teeth" before she died of fever last week. A drunk fisherman, Old Cray, mutters about "the Deep Hymn" and how "it calls the faithful down."
Night Event: As the party rests, they hear it,a low, resonant thrumming from beneath the earth. It's almost musical, but it makes their bones vibrate uncomfortably. Constitution saving throw (DC 12) or be unable to sleep well (disadvantage on first check tomorrow). The druid might recognize this as deeply unnatural,no animal or natural phenomenon makes this sound.
The Widow's Point Lighthouse (1.5 hours)
A mile up the coastal cliffs. The lighthouse is dark, door ajar. Blood trails lead inside.
Exterior: Tide pools around the base are filled with dead crabs, all facing the same direction,toward the sea. Survival check (DC 13) reveals webbed, clawed tracks leading from the water to the lighthouse.
Interior - Ground Floor: The main chamber reeks of brine and rot. Furniture is overturned. Claw marks on the walls. A journal lies open:
"Day 40: The hymn grows louder. I see them in the water now,pale shapes, swimming in circles. They're waiting.
Day 43: Aldous has stopped eating. He sits by the window, watching. He says 'Mother calls.'
Day 44: I hear scratching at the door. Aldous is gone. I've barricaded myself upstairs. If anyone reads this,don't go into the water. Don't listen to the,"
The entry ends in a smear of blood.
Encounter 1: The Drowned Ones (CR 4 total)
Tactics: They try to grapple and drag victims toward windows/water. The rogue can pick them off from range; the barbarian can break grapples; the paladin's radiant damage causes them to shriek.
Loot: Aldous wears a silver lighthouse keeper's medallion (worth 50gp, but radiates faint abjuration magic,can be used as a component for protection from evil/good).
Upper Lighthouse: The lamp chamber is shattered. At the center is a makeshift altar,bones arranged in a spiral pattern, all facing a crude carving of something with many heads.
Investigation (DC 14): The bones are recent. Human. Arranged in a pattern that resembles tidal charts.
Religion (DC 13): This is a summoning circle, but degraded. Whatever was called didn't need much convincing,it was already close.
Religion (DC 16): The symbol matches ancient texts about the Drowned Gods,primordial horrors that predate modern deities.
Nature (DC 15 - Druid advantage): The bones show signs of rapid mutation before death,extra joints, gill formations, scale growth. This isn't a disease. It's a transformation.
First Godly Weapon - The Paladin's Gift:
Hidden beneath the altar bones is a locked iron coffer (Rogue can pick, DC 15, or it can be smashed open AC 19, HP 15).
Inside: Tidebreaker, a longsword with a blade that seems to shimmer like sunlight through water. The crossguard is shaped like breaking waves.
Tidebreaker (Longsword, requires attunement by a paladin)
The blade feels right in the paladin's hands, warm and steady. A voice,not quite sound, more like a memory,whispers: "Stand against the deep."
The Cliff Descent (30 minutes)
From the lighthouse, the party can see it: a massive cave entrance at the waterline, only accessible at low tide. The thrumming sound emanates from within.
Skill Challenge: Getting down the 200-foot cliff safely.
At the bottom, the tide pools are filled with pieces,chunks of whale blubber, shark teeth the size of daggers, fish heads with too many eyes.
Cave Entrance: Wide enough for three people abreast. The walls glisten with a phosphorescent slime (harmless, but eerie,casts green-blue light). The thrumming is louder here, almost rhythmic.
ACT II: THE FLOODED HALLS (Hours 3-6)
The Sunken Temple (1 hour)
The cave opens into a vast, partially flooded chamber,clearly not natural. Crumbling pillars carved with maritime scenes (ships, krakens, drowning sailors) hold up a ceiling 40 feet high. The water is 3 feet deep, murky, and warm.
History (DC 14): This is pre-human. Sahuagin? No,older. The architecture predates known civilization.
Arcana (DC 15): The carvings aren't decorative. They're instructional,depicting a ritual to "call the Mother of Depths."
Perception (DC 13): Something large moves beneath the water. Multiple somethings.
Encounter 2: Hydra Spawn (CR 6 total)
Tactics: They emerge from the water, serpentine bodies coiling. They try to separate the party, using the pillars as cover. The warm water is difficult terrain. The rogue can use pillars for advantage; the druid might control water or wild shape into something amphibious; barbarian rage resists the acid; paladin's radiant damage cauterizes, preventing the acid spray.
Loot: Among the bones at the bottom: 200gp in old coins, a pearl of power, and a waterlogged spellbook containing control water and water breathing.
LEVEL UP TO 6
The Breeding Pits (1.5 hours)
Beyond the temple, the tunnel slopes downward. The water deepens to 4 feet, then 5. The thrumming is now accompanied by wet, slithering sounds.
The passage opens into a nightmarish cavern: dozens of fleshy sacs attached to the walls and ceiling, each the size of a horse. They pulse rhythmically. Inside, shadowy shapes twist.
Nature/Medicine (DC 14): These are eggs. Gestation sacs. Whatever's inside is nearly ready to hatch.
Arcana (DC 13): The magic here is overwhelming,transmutation and conjuration, twisted together. This place is a factory of corruption.
At the center of the chamber, tending the sacs, is The Shepherd,a hulking sahuagin corrupted beyond recognition. Its body is covered in additional mouths that whisper in Aquan: "Mother feeds us. Mother loves us. We are her children."
Encounter 3: The Shepherd (CR 6)
Add:
Tactics: The Shepherd fights defensively, using the sahuagin as shields while trying to frighten the party. It retreats toward the eggs if bloodied, trying to rupture them to release premature spawn (if an egg is destroyed, a malformed hydra spawn emerges but only has 30 HP and one head).
Second Godly Weapon - The Druid's Gift:
After the battle, one of the egg sacs pulses differently,greener, with vines growing through it. It's been corrupted differently, nature trying to fight back.
Inside: Rootcaller, a quarterstaff of living wood that blooms with tiny white flowers.
Rootcaller (Quarterstaff, requires attunement by a druid)
The wood thrums with life, warm and vital against the corruption surrounding it. The druid can feel the ancient forests speaking through it: "Life endures."
The Drowned Gallery (1 hour)
A long, descending tunnel. The water is now chest-deep (difficult terrain for non-aquatic movement). The walls are covered in carvings,an entire history:
History (DC 16): This is the Covenant of Chains,a thousand years ago, a circle of druids and clerics bound the thessalhydra here, using the natural rock and blessed anchors. But the bindings have failed.
Investigation (DC 14): The recent carvings are... worshipful. Someone has been coming down here, celebrating the hydra's return.
Ahead, candlelight flickers.
Encounter 4: The Cult (CR 7 total)
A chamber opens up, dry, with a raised platform. Here, High Cultist Maren (human woman, eyes replaced with black pearls) leads a group in prayer.
Tactics: Maren casts spirit guardians immediately (the drowning hands create difficult terrain and deal 3d8 damage). She uses hold person on martial characters while cultists swarm the held targets. The cultists fight to the death, screaming hymns.
Roleplay opportunity: If Maren is captured/questioned:
Loot:
LEVEL UP TO 7
ACT III: THE FEEDING DEEP (Hours 6-9)
The Anchor Chambers (1.5 hours)
Following the map, the party reaches a series of three chambers, each containing one of the ancient anchors used to bind the thessalhydra. Each is a massive stone pillar carved with divine symbols, glowing faintly with failing magic.
The water here is deep,10 feet in most places, requiring swimming (the ring of water walking helps, as does water breathing if the party prepared it).
Each chamber has a guardian,remnants of the binding ritual, now corrupted:
Chamber 1: The Chained Druid
The druid's face is visible in the trunk, screaming silently. If the party destroys the anchor after defeating the treant, the druid's spirit is released and whispers a warning: "Eight heads. Eight hungers. It cannot die while even one feeds."
Chamber 2: The Blessed Sentinel
The naga was once a guardian of the binding. Now it serves the hydra. It fights intelligently, using counterspell against healing and blight against the druid.
Chamber 3: The Drowned Knight
This was once a hero. Now its armor is rusted, face skeletal, eyes burning with cold fire. It doesn't speak, just attacks with mechanical precision.
Third Godly Weapon - The Barbarian's Gift:
When the knight falls, its armor crumbles to rust. But its weapon remains: Stormbreaker, a greataxe crackling with primal fury.
Stormbreaker (Greataxe, requires attunement by a barbarian)
The axe feels like a thunderstorm contained in steel. When the barbarian grips it during rage, lightning arcs between their fingers. It roars for battle.
The Feeding Grounds (45 minutes)
With the anchors destroyed, the way to the thessalhydra's lair is open. A massive tunnel, 30 feet wide, slopes down into darkness. The thrumming is now deafening,a physical pressure against the ears.
The water rushes downward, creating a current. The party must navigate carefully (Athletics checks DC 13 or be swept along, taking 2d6 bludgeoning from impacts).
The tunnel opens into a vast cavern,the Feeding Grounds. Here, the thessalhydra has dragged its kills. The floor is a charnel pit: whale bones, ship wreckage, human remains by the hundreds. The water is thick with blood.
Perception (DC 12): Movement in the bones. Something large.
Encounter 5: The Bonecrusher (CR 8)
This creature has been feeding on the hydra's scraps, growing massive. It erupts from beneath the bones, superheated from the hydra's proximity.
Tactics: It tries to swallow the highest-damage dealer (likely the barbarian), then burrow away to digest. The rogue can attack from range; the paladin and druid must avoid the heated body while dealing damage. If it swallows someone, the party must decide whether to focus fire or try to force regurgitation.
Fourth Godly Weapon - The Rogue's Gift:
Among the treasures in the bone pile:
Shadowfang (Pair of daggers, requires attunement by a rogue)
The daggers feel weightless, extensions of shadow. When the rogue holds them, they seem to blur at the edges, as if not entirely present in this reality.
ACT IV: THE MOTHER OF DEPTHS (Hours 9-10)
The Thessalhydra's Lair (1 hour, 15 minutes)
Beyond the Feeding Grounds, a massive archway,clearly artificial, carved with warnings in a dozen dead languages. All say variations of: "SEALED BY COVENANT. DO NOT BREAK THE CHAINS. THE MOTHER MUST NOT WAKE."
The archway leads to a cathedral-sized cavern. The ceiling is lost in darkness above. A vast pool dominates the center, 50 feet across, water black as ink. Around the pool's edge: the broken remains of the three anchors, their chains snapped.
The thrumming stops.
Silence.
Then: "You... come... to... feed... Mother?"
The voice comes from everywhere and nowhere,eight voices speaking in unison, overlapping, creating a nauseating harmony.
The thessalhydra rises.
FINAL ENCOUNTER: The Thessalhydra (CR 11)
Thessalhydra (Legendary)
Abilities:
Special Traits:
Eight Heads: The thessalhydra has eight heads. While it has more than one head, the thessalhydra has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.
Whenever the thessalhydra takes 30 or more damage in a single turn from a single source, one of its heads dies. If all its heads die, the thessalhydra dies.
At the end of its turn, it grows two heads for each head that died since its last turn, unless it has taken radiant damage since its last turn. The thessalhydra regains 15 hit points for each head regrown this way. (Maximum 12 heads total)
Multiple Heads: The thessalhydra can take one reaction per head.
Reactive Heads: For each head beyond one, the thessalhydra gets an extra reaction that can be used only for opportunity attacks.
Wakeful: While the thessalhydra sleeps, at least one of its heads is awake.
Aquatic Advantage: The thessalhydra has advantage on attack rolls while both it and its target are in water.
Psychic Hymn (Aura): At the start of each of the thessalhydra's turns, all creatures within 30 feet must succeed on a DC 16 Wisdom saving throw or take 2d6 psychic damage and have disadvantage on attack rolls until the start of the thessalhydra's next turn.
Actions:
Multiattack: The thessalhydra makes as many bite attacks as it has heads (starting with 8).
Bite: Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 1d10+6 piercing damage.
Acid Spray (Recharge 5-6): The thessalhydra sprays acid in a 30-foot cone from one of its heads. Each creature in that area must make a DC 16 Dexterity saving throw, taking 6d6 acid damage on a failed save, or half as much on a successful one.
Grasping Tentacles (Recharge 6): Four tentacles erupt from the thessalhydra's body. Each tentacle attacks one creature within 20 feet (+10 to hit, 2d6+6 bludgeoning damage, target is grappled, escape DC 16). While grappled, the target takes 2d6 bludgeoning damage at the start of each of its turns. The thessalhydra can grapple up to four creatures this way.
Legendary Actions (3 per round):
Detect: The thessalhydra makes a Wisdom (Perception) check.
Bite Attack: The thessalhydra makes one bite attack.
Thrashing Coils (Costs 2 Actions): The thessalhydra thrashes its massive body. Each creature within 10 feet must succeed on a DC 16 Strength saving throw or take 3d8 bludgeoning damage and be knocked prone.
Submerge and Strike (Costs 3 Actions): The thessalhydra submerges into the pool (if in water) or slithers to a new position (if on land), moving up to its speed without provoking opportunity attacks, then makes a bite attack with advantage.
The Battle:
Phase 1 (HP 280-200): The thessalhydra fights cautiously, using its reach and multiple attacks. It focuses on spreading damage across the party, testing their defenses. Uses legendary actions for bite attacks primarily.
Phase 2 (HP 199-100): The thessalhydra becomes aggressive. Starts using Acid Spray whenever available. Uses Grasping Tentacles to isolate targets (tries to grapple casters/ranged attackers and drag them into the water). Heads begin to die and regrow,unless the party uses radiant damage (Paladin's Tidebreaker or spells).
Phase 3 (HP 99-0): Desperate and enraged. The thessalhydra uses Thrashing Coils frequently (costs 2 legendary actions). If reduced below 50 HP, it tries to swallow a character whole (use modified swallow: one head can attempt to swallow one Medium or smaller creature that is grappled by tentacles,Strength save DC 16 or be swallowed. Swallowed creature takes 4d6 acid per turn and grants the thessalhydra +2 AC as a "shield").
Environmental Hazards:
Tactical Considerations for the Party:
The key: recognize that radiant damage stops regeneration. Cut off heads faster than they grow back. Manage the grapples (the bound character or an ally must break free). Survive the psychic aura (spread out or use calm emotions if available).
Victory and Aftermath (15 minutes)
When the thessalhydra finally dies, its body dissolves into black ichor that evaporates with a sound like screaming. The psychic hymn stops,the sudden silence is almost painful.
The cavern begins to collapse,the thessalhydra's presence was holding the structure together.
Skill Challenge: Escape
Success: They emerge from the lighthouse cave as the cliffside collapses into the sea. The thrumming is gone. The water is clear.
Failure: They escape but take 4d10 bludgeoning damage from cave-ins and near drowning.
Epilogue:
The party returns to Gallowmere at dawn. The sun is rising,something the townspeople haven't seen clearly in months.
Miriam Salt greets them, tears in her good eye. The fish have returned to the nets. Children slept peacefully last night for the first time in weeks.
Rewards:
I think you're planning out your players' actions too much. What level is the party supposed to be?
Find your own truth, choose your enemies carefully, and never deal with a dragon.
"Canon" is what's factual to D&D lore. "Cannon" is what you're going to be shot with if you keep getting the word wrong.
I'd say you've got a great adventure frame here. I have two things I'd point out though.
1 - This is a pretty 'on rails' adventure. It is very linear. That's not necessarily a bad thing, but are preparing too for player characters to try unusual courses of action? If no, I'd suggest trying to consider some other options. What for example if the party decide simply to collapse the cave entrance, deciding that 'hey this is the best way of sealing the dangers within'?
2 - What is the motivation for the party? Is there an imminent danger to the characters? Is the final boss really that much of a risk? The stakes here don't really seem to provide a motivation for the player characters beyond them being heroes and wanting to do 'good deeds'. I've had player characters in the past who would look at the potential dangers, shrug and simply set up a town hall meeting to convince the civilians to abandon their homes and leave this tainted place.
To be clear, there's a lot of good thought here, and some parties LOVE a linear experience. I have some players who just cannot deal with an open world and infinite choices. I've got other players who need to know they've got the options to do whatever chaotic thing pops into their mind. It'll depend on the table, but I'd say you've got a great outline for a solid adventure.
DM session planning template - My version of maps for 'Lost Mine of Phandelver' - Send your party to The Circus - Other DM Resources - Maps, Tokens, Quests - 'Better' Player Character Injury Tables?
Actor, Writer, Director & Teacher by day - GM/DM in my off hours.
Several comments.
1) It is a wonderful outline. Just remember that your players won't necessarily do as you expect.
2) As far as I can tell, they are level 7 for the final encounter since there are no level ups listed past Act III. You're thinking appears to be that the Paladin would have Crusader's Mantle as a prepared spell and would have both the spell slot and the spell available for the final encounter.
- Paladin's don't get 3rd level spells until 9th level.
- Crusader's Mantle is a 3rd level spell and the character will have at most 2 third level slots.
- the encounter plan does not seem to have a long rest between Act III and Act IV so the characters would likely be down both hit points and spell slots coming into the final encounter - likely making your ideas of how the party might deal with the encounter invalid.
The paladin has 2 attacks - radiant damage prevents regeneration but what happens if the paladin misses? What happens if the hydra hits the paladin and they lose concentration on Crusader's mantle. The hydra gets one attack/head starting with 8! Assuming it is an intelligent creature, why would it choose to spread attacks around and not try to take down a character as quickly as possible (other than the fact it isn't fun for the player?).
3) You mention the druid turning in to elementals. This assumes you are playing the 2014 version of 5e AND that the druid is at least a level 10 moon druid - which can already shape shift as a bonus action ... the option isn't available before then. The rootcaller description doesn't seem to give the druid additional wildshapes. Using the 2024 rules, shifting into an elemental isn't an option. So, I am not sure what you are thinking here unless a bunch of house rules are involved.
4) Killing a head requires 30 or more damage on a single turn from a SINGLE source. The only martial builds (paladin, rogue or barbarian) that I've seen that might be able to do that are 2014 Great Weapon Master and Sharpshooter builds and even then they would rarely hit 30 damage from a single attack. On the other hand, perhaps you mean total damage from an individual character - this is more doable but still challenging.
Anyway, the hydra encounter seems to me like a possible recipe for a TPK given the outline for the adventure.
P.S. 8 attacks at +10 doing d10+6 ... will add up quite quickly. For a 20 AC character - about 50% will hit every turn doing an average 46 damage - which is probably almost enough to take out some level 7 characters. Level 7 rogue with 12 con would be 45.
Tidebreaker gives free crusaders mantle no concentration required.