Hold Breath. The undead nagasuar does not need to breathe.

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

Whenever the nagasaur takes 30 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 acid damage since its last turn. The undead nagasaur regains 10 hit points for each head regrown in this way.

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

Undead. The undead nagasaur does not need to sleep, eat, or drink.

Multiattack. The undead nagasaur makes as many bite attacks as it has heads.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one creature. Hit: 12 (2d6 + 5) piercing damage plus 10 (3d6) poison damage.