“Yes but it will fall on deaf ears, they fight even among themselves and don’t hesitate to attack if numbers favor them.”  Eron would love to charge in use his black hat and even the numbers but with such great recon and casters he is holding back to hear some ideas first.  He draws his long sword and bone dagger to the ready.

"Since I get the strong impression they lay in ambush I doubt we will get the chance to communicate with them before they attack. Taking a prisoner to interrogate would probably be a good idea though." Arlynn suggests. "To me the question is if we let them start the fight or if we start it by luring them out and then attacking them from a distance? No immediate hurry though, cast your spell Fane, it might be useful either way."

Eron waits while Fane renews her spell.  “Well I will happily spring their ambush, that way you three can attack at range.”  If everyone seems ready Eron assumes a defensive ready stance and heads in to the Ambush area…

As the team eventually proceeds and gets within 90 feet from the ambush position, Arlynn will motion for the team to form up in a defensive position and then summon a spectral tentacle to go bullywug hunting, sending it forward, using her familiar's sight if necessary to spot her target, letting it thrash at a bullywug to get it out of hiding, ready to launch a barrage of eldritch blasts from behind a tree.

(Tentacle: 12 Cold: 8 speed is reduced by 10 feet until the start of next turn)

Fane completes her ritual while the rest of the party talks strategy for 10 minutes.  Then, prepared for violence or diplomacy, they advance closer.

Eron steps carefully along the muddy shoreline, his every sense on high alert as he neared the suspected ambush site.  The marsh is as still as it had been since they began this excursion, save for the occasional distant croak or rustling of reeds.  The dark water beside him lay stagnant and silent, its surface mostly smooth.  Here and there, he spots what Arlynn's familiar must have seen.  Traces of movement.  He has time to observe that they don't look quite like bullywugs, or crocodiles.  More fish or snakelike.  Giant constrictors, maybe?

Initiative:  

• Arlynn:  19
• ???:  10
• Fane:  9
• Eron:  7
• Lyrric:  4

Ninety feet back, Arlynn has hung behind with Lyrric and Fane, her eyes narrowing as she focused on one of the indistinct shapes beneath the water.  Following the plan, she summons her magic, a spectral, writhing tentacle lashing out toward the lurking figure.

The impact iss immediate.  The water thrashed violently as the shape beneath recoiled.  But it was not the response of a startled bullywug.  No guttural croak, no humanoid figure leaping from the reeds with a spear in hand.  Instead, a deep, reverberating growl bubbled up from beneath the surface.  Then another shape surged.  Ripples became waves.  The once-still water churned, swirling in angry eddies as something massive began to rise.

Eron barely had time to register the disturbance before the first head broke the surface.  A long, serpentine neck arched skyward, its thick, scaled hide gleaming wetly in the sunlight.  Yellow reptilian eyes snapped open, scanning the canal with fury.

Then another head rose.

And another.

And another.

Water cascaded off its writhing forms as the adolescent hydra fully emerged, its many necks twisting and coiling in agitation.  It was not yet the towering behemoth of legend, but even in its youth, this beast dwarfs Eron.

It let loose a guttural, multi-voiced hiss, its heads flicking side to side, searching for the source of its pain.  But its gaze quickly settled on the closest intruder—Eron.

Round One:

1. Arlynn
2. Adolescent Hydra
3. Fane
4. Eron
5. Lyrric

"Oh dear..." The blue-haired half-elf says with suprise and awe in her wide eyes. She knew there were monsters in the marshes, she just didn't expect one quite as monstrous as this one. She couldn't help but wonder if the hydra had moved here recently or Usk could have cared to mention it's presence here. Either way it was probably best to rid the marsh of it.

Snapping out of her brief thoughts, Arlynn lets her tentacle thrash at the many-headed monster once more.
Tentacle: 15 Cold: 6 speed is reduced by 10 feet until the start of next turn

She then unleashes a azure beam of eldritch crackling force towards the hydra.
Eldritch Blast: 16 Force: 15

"Eron, fall back!" She calls out to their captain in a worried tone.

(Also, for what it's worth, the tentacle would have moved to interpose itself between Eron and the hydra :-)

After Arlynn's magical attacks, two of the hydra's five heads hang limp and dead.  The other three snap ineffectively at the tentacle, then turn their focus back on Eron.  It swims slowly through the water, hauling its bulk up onto the beach 20' away from Eron.

Fane, Eron and Lyrric are up!

On his turn, Eron uses his intuitive hunter’s sense to discern how best to defeat this brute.  He also casts hunter’s mark letting his focus settle solely on the hydra.  Lastly he moves 30’ back along the waterline drawing the behemoth closer to his companions and its destruction.

Eron:

Fane will move 30 ft to the north, Leo still with her, and then send a bolt of fire at the Hydra.

Fire bolt: 20 for 10 fire damage.

Lyrric took a moment to doff his shield and moved to a place that he had a shot with his crossbow.

Move 25' north, looking to end in a square where ranged attacks are possible. 
Doff shield (as utilize action), equip crossbow (free item interaction).

Relieved to see Eron pull back, the blue-haired half-elf again lets her slithering tentacle slide after the many-headed monstrosity through the water and thrash at it once more.
Tentacle: 18 Cold: 6 speed is reduced by 10 feet until the start of next turn

She then unleashes another azure beam of eldritch crackling force towards the hydra, changeing position as needed to get a clear shot.
Eldritch Blast: 20 Force: 7

She then falls back a bit further to keep a healthy distance to the advancing terror.

As Fane and Arlynn continue to hammer the large monstrosity with spells and cantrips, two more of its heads slump over, dead.  The lumbering creature halts on the beach.  Only a single head remains.  It turns, abandoning its pursuit of these little, stinging prey, and returns to the deeper water in the middle of the canal and submerges.

[The young hydra is fleeing.  If anyone wants to press the attack, it is back in the middle of the canal, underwater.  Hidden beneath the surface it has 3/4 cover from attacks.  Otherwise we are out of initiative.]

The blue-haired half-elf looks over at her three companions, waiting to see if they should pursue or let the monstrosity escape. 
"Your orders captain?" She calls out to Eron.

"I vote we leave the beast alone and move on, no reason to waste resources on it" Fane says.

The battle had been swift but brutal, but thankfully they’d driven the creature off.

Lyrric made an adjustment on his crossbow, making sure it was in working order, eyes scanning the murky waters and tangled reeds for any sign of their true quarry.

"If I were a bullywug ..." He murmured, half to himself, half to his companions.

"I’d be watching from the shadows right about now, waiting to see if that hydra did my work for me."

Will travel from this point forward with crossbow equipped, shield stowed.

No sooner does Lyrric voice his thoughts, then—before they could even sheathe their blades—a sudden whoosh cut through the air.  Spears.

Not aimed at the party, but at the still-writhing shape beneath the water.

One after another, barbed wooden shafts rain down from the tall reeds along the canal.  The muddy banks explode with movement, and guttural croaks of triumph echo through the marsh.  The spears find their mark, piercing deep into the hydra’s submerged form.  With a final convulsion, the beast expires and drifted, belly-up, to the surface.

From the tall grass, a force of bullywugs reveal themselves.  They are grotesque creatures, like massive, humanoid bullfrogs.  Their bodies were slick with moisture, their bulbous eyes glinting in the dim light.  They moved with lurching speed, their long, powerful legs carrying them forward in great hops as they emerge from the reeds and grasses that surround the canal.

There are ten in all, but three stood apart.

The first, an eerie, hunched figure, clutched a staff adorned with a hornets’ nest hanging from the end, its surface still crawling with restless, buzzing insects.  Its leathery skin was dried by the sun and covered in dark, ceremonial markings, and its wide, glassy eyes gleamed wildly. 

The second was larger than most, its sagging, distended throat pouch quivering as it moved.  Unlike its mostly nude kin, it wore crude armor made from the stitched pelts of small mammals.  It carried a jagged axe, and its wide mouth curled into a smug sneer.

The last was unmistakably their leader.  Seated atop the massive, warty back of a giant toad, the creature exuded an air of disgusting royalty.  It was the largest of them all, its bloated frame draped in a filthy, half-rotten cloak.  Upon its broad head sits a gleaming steel helmet - it is fastened by a woven strap as the king's head isn't properly proportioned to fit inside - clearly looted from some unfortunate knight.  In its webbed hand, it carried a long staff of black wood, while the other gripped a battered wooden shield.  From its mount, the King surveyed the party with a regal croak of triumph.

Then, the bullywug in hide armor stepped forward, its throat pouch expanding with a wet gurgle before it spoke in broken Common.

“Kneel!  Kroak!  Kneel before mighty King Gulpa’Gor, first of his name, ruler of all lands—green, brown, and grey!”  It gestured grandly to the floating corpse of the hydra.  “This questing beast—our kill!  Our prize!  KROAK!!  You surrender now - you join it in bellies of the bullywugs!  Kroooooak!”

All around them, the other bullywugs brandished their weapons, their throats puffing up, eyes bulging with anticipation.  They begin to advance on the party.

Initiative:

1. Eron:  17
2. Bullywug Leaders:  14
3. Bullywugs:  13
4. Fane:  12
5. Arlynn and Lyrric:  6

“Oh great King Gulpa’Gor.  You could easily crush us few here and now.  Or you could test your great warriors and see a great entertaining fight.  I will fight any warrior you choose what do you say Great Kroaker King Gulpa’Gor?”

persuasion to fight as entertainment (a distraction and opportunity for a spontaneous plan)  14

bonus action to move the hunter’s mark to the bullywug in hide armor

11

The king seems to briefly consider Eron's offer...