Hydra

Hydras are huge reptilian monstrosities with multiple heads.

Appearance
Hydras are chiefly identified by their multiple heads. The hydra near Vasselheim had a scaled, tan/dark-brown hide and a long tail, and purplish blood.

Characteristics and abilities
Assumed Hit Points: 379-388 (Took 428 damage; Regenerated 40 [8 heads regrown for 5 HP each])

Armor Class: 15

Abilities
Multiple Heads: The hydra has five heads. While it has more than one head, the hydra has advantage on Saving Throws against being Blinded, Charmed, Deafened, Frightened, Stunned, and knocked Unconscious.

Whenever the hydra takes 25 or more damage in a single turn, one of its heads dies. If all its heads die, the hydra 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. The hydra regains 10 Hit Points for each head regrown in this way.

Wakeful: While the hydra sleeps, at least one of its heads is awake.

Actions
Multiattack: The hydra makes as many bite attacks as it has heads.

Bite: Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) piercing damage.

Known hydras
Vox Machina encountered a hydra just outside Vasselheim; killing the hydra without sanction resulted in their introduction to the Slayer's Take, and thereby to Osysa, who informed them of the Vestiges of Divergence.

On Urukayxl in the Temple of the False Serpent, the Mighty Nein defeated the hydra who guarded one of the seals of Uk'otoa.

In the story hook Unfriendly Waters in both the Tal'Dorei Campaign Setting and Tal'Dorei Campaign Setting Reborn, there is a hydra in Mooren Lake whose intelligence has been augmented by the residuum runoff and who commands a nearby tribe of lizardfolk.