Crowmetheus

Amphibious. The Crowmetheus can breathe air and water.

Legendary Resistance (3/Day). If Crowmetheus fails a saving throw, it can choose to succeed instead.

Multiple Heads. Crowmetheus has five heads. While it has more than one head, Crowmetheus has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Whenever Crowmetheus takes 25 or more damage in a single turn, one of its heads dies. If all its heads die, Crowmetheus dies.

At the end of its turn, it grows two heads for each of its heads that died since its last turn, unless it has taken fire damage since its last turn. Crowmetheus regains 10 hit points for each head regrown in this way.

Reactive Heads. For each head Crowmetheus has beyond one, it gets an extra reaction that can be used only for opportunity attacks.

Wakeful. While Crowmetheus sleeps, at least one of its heads is awake.

Multiattack. Crowmetheus can use its Frightful Presence. It then makes one bite attack and two claw attacks. It may use its Crush or Swallow in place of its bite.

Bite. Melee Weapon Attack: +12 to hit, reach 25 ft., one target. Hit: 43 (6d10 + 10) piercing. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and Crowmetheus can't bite another target.

Claw. Melee Weapon Attack: +12 to hit, reach 20 ft., one target. Hit: 31 (6d6 + 10) slashing damage.

Crush. Crowmetheus attempts to crush its foes underneath it using its weight. All creatures in Crowmetheus' space must make a DC 19 Dexterity saving throw. On a success, a creature is not crushed, and moves out of Crowmetheus' space to a space adjacent to Crowmetheus. On a failure, a creature becomes grappled by Crowmetheus (escape DC 20). While grappled in this manner, a creature is also considered prone and restrained, and takes 37 (6d8 + 10) bludgeoning damage at the start of each of Crowmetheus' turns. A creature is freed from this grapple when Crowmetheus moves.

Swallow. Crowmetheus makes one bite attack against a Colossal or smaller creature it is grappling. If the attack hits, the target takes the bite's damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside Crowmetheus, and it takes 44 (11d8) acid damage at the start of each of Crowmetheus' turns.
If Crowmetheus takes 60 damage or more on a single turn from a creature inside it, Crowmetheus must succeed on a Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of Crowmetheus. The DC for this saving throw equals one-third the damage taken during that single turn. If Crowmetheus dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

Frightful Presence. Each creature of Crowmetheus' choice that is within 240 feet of Crowmetheus and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Crowmetheus' Frightful Presence for the next 24 hours.

Prismatic Breath (Recharge 5-6). Crowmetheus exhales prismatic energy in a 150-foot cone, which manifests as eight multicolored rays of light. Each ray is a different color and has a different power and purpose. Each creature in the area of effect must make a DC 30 Dexterity saving throw, and each creature also rolls a d8 to see which color ray affects them:

1. Red. The target takes 130 (20d12) fire damage on a failed save, or half as much damage on a successful one.

2. Orange. The target takes 130 (20d12) acid damage on a failed save, or half as much damage on a successful one.

3. Yellow. The target takes 130 (20d12) lightning damage on a failed save, or half as much damage on a successful one.

4. Green. The target takes 130 (20d12) poison damage on a failed save, or half as much damage on a successful one.

5. Blue. The target takes 130 (20d12) cold damage on a failed save, or half as much damage on a successful one.

6. Indigo. On a failed save, the target is restrained. It must then make a DC 20 Constitution saving throw at the end of each of its turns. If it successfully saves three times, the spell ends. If it fails its save three times, it permanently turns to stone and is subjected to the petrified condition. The successes and failures don't need to be consecutive; keep track of both until the target collects three of a kind.

7. Violet. On a failed save, the target is blinded. It must then make a DC 20 Wisdom saving throw at the start of the Crowmetheus' next turn. A successful save ends the blindness. If it fails that save, the creature is transported to another plane of existence of the DM's choosing and is no longer blinded. (Typically, a creature that is on a plane that isn't its home plane is banished home, while other creatures are usually cast into the Astral or Ethereal planes.)

8. Special. The target is struck by two rays. It rolls twice more, rerolling any 8's.

Bloodied Breath. When Crowmetheus falls below half its hit point maximum, it uses its prismatic breath. Crowmetheus does not need to have its prismatic breath charged, and using its breath in this manner does not consume its charge. Once Crowmetheus uses this reaction, it can't use it again until it reaches its hit point maximum.

Crowmetheus can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Crowmetheus regains spent legendary actions at the start of its turn.

Detect. Crowmetheus makes a Wisdom (Perception) check.

Wing Attack (Costs 2 Actions). Crowmetheus beats its wings. Each creature within 10 feet of Crowmetheus must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. Crowmetheus can then fly up to half its flying speed.