Hold Breath. Grandlejaw can hold its breath for 1 hour.

Multiple Heads. Grandlejaw 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 Grandlejaw 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. Grandlejaw regains 10 hit points for each head regrown in this way.

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

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

Multiattack. Grandlejaw 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.