Hold Breath. The hydra can hold its breath for 1 hour.

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.

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

Vitriolic Reaction. If the hydra loses a head, its acid spit recharges.

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

Multiattack. The hydra makes as many bite attacks as it has heads. If it can use its acid spit, it can substitute it for one of the bite attacks.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 5) piercing damage and 7 (2d6) acid damage.

Acid Spit (Recharge 5–6). The hydra spits acid at a point it can see within 40 feet of it. Each creature within 10 feet of the point of impact must make a DC 16 Dexterity saving throw, taking 21 (6d6) acid damage on a failed save, or half as much damage on a successful one.