Hold Breath. The hydra can hold its breath for 1 hour.
Multiple Heads. The hydra has five 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: +8 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) piercing damage.
Description
The hydra is a reptilian horror with a crocodilian body and multiple heads on long, serpentine necks. Although its heads can be severed, the hydra magically regrows them in short order.
172 average HP
With a party of 5
You would be able to take this thing down easily IF
No one goes down in the second round and Everyone does atleast 25 damage
@KaptainKittens
I animated a skeletal one and did this. By the time I reached the final boss 18 sessions later, my skeletal hydra (created with Animate Dead) had 630 heads. That's an average of 6615 damage per round if all attacks hit. The final boss was a tarrasque. It did not survive the Hydra's turn.
*cough cough Frost Brand cough cough*
Hai Hydra! Hail Hydra! Hail Hydra!