Crying 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 or force damage since its last turn. The hydra regains 15 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 and life overload attacks as it has heads.

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 5) piercing damage.

Life Overload (Recharge 5-6 Per Head). The Hydra launches a beam of light from one of it's mouths in a 10 ft. wide, 100 ft. long line. Every creature within this line must make a DC 20 Dexterity save or take 20 (4d10) radiant damage on a failed save and become stunned until the end of the creature's next turn, but regaining 10 (4d6) hit points on a successful one.  

Wailing Screech (Recharge 5-6). The Crying Hydra lets out a vicious screech; all creatures within 50 ft. of the Hydra must succeed a DC 16 wisdom saving throw or take 9 (3d6) thunder damage and become Frightened for the duration of the creature's next turn. On a successful save, the creature takes half as much damage and has disadvantage on attack rolls during it's next turn.