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

Multiple Heads. The hydra has 4 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.

If the a head dies another one sprots out and you decide if it cut of a head then pay attenuation to the number if 4 or over does not cut off head if  roll 3 or lower then another head sprouts out.

Reactive Heads. For each head the hydra 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.

Fly can fly 40 feet every turn

Multitask. The hydra makes as 4 bite attacks .

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

Explosion one head can breathe gas and one can light it. It does 2d12 damage and every body has to do it. Can breath out 80 feet radius feet of gas every turn . If the both ga head do it then 160 feet and if both spark heads are doing it the explosion does 4d12 damage.