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

Whenever the hythid takes 25 or more damage in a single turn, one of its heads that was not grown twelve or more hours ago  dies. If all its heads die, the hythid dies.

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

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

Multiattack. The hythid 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.

Swallow. Five times a day, the hythid can choose to grapple one creature within 60 feet of it with DC 16. If suceeded, the hythid's round is over. If failed, the hythid swallows the creature whole. After 5 rounds, the swallowed creature's ability scores all become zero and the hythid grows a new head that contains the consciousness of the swallowed creature except the strength, dexterity, and constitution ability scores of the swallowed creature become that of the hythid's as well as the alignment.This can be reversed if the hythid diesdies or the swallowed creature is removed from the hythid's gut, but both must be done before twelve hours have passed. Otherwise, it is only reversible with a wish spell or simular magic.