Cursed Hydra

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

Multiple Heads. The hydra has four 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.

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.

Bite. Melee Weapon Attack: +5 reach 10 ft., one target. (1d8 + 3) piercing damage.

Ghoulish Burst (recharge 6): A green acid like flame covers 4 eyes of the hydra. Both heads rap together shooting a ghostly energy at any creature in range. Ranged weapon attack: DC: 15 Con save 100 ft straight line (4d10+4) necrotic and half on a successful save.

Tail spine (1/day). Demonic horns shoot out of it's tail and it swings the tail violently as the Hydra screeches in pain. Melee weapon attack: +8 who over is in a 30 foot cone, (2d10+4) acid damage.

Ghostly preservation (1/day). A many souls of different origins busts into the scales revealing the ghostly curse granting a +2 to AC until the start of it's next turn.