Eel Hydra (5e Creature)
From D&D Wiki
Huge monstrosity, unaligned
Hold Breath. While out of water, 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.
Static Pulse. A creature that touches the eel hydra or hits it with a melee attack while either the hydra or creature is on land and within 5 feet of it takes 3 (1d6) lightning damage. If both the hydra and the creature are underwater, then the range is increased to 10 feet and the creature takes the damage whether it hits or misses. This does not stack with the additional lightning damage from the hydra's bite attack.
Wakeful. While the hydra sleeps, at least one of its heads is awake.
Water Breathing. The hydra can breathe only underwater.
Multiattack. The hydra makes as many bite attacks as it has heads.
Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) piercing damage and 3 (1d6) lightning damage.
Constrict. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 13 (2d8 + 5) bludgeoning damage. The target is grappled (escape DC 18). Until this grapple ends, the creature is restrained, and the hydra can't constrict another target.
The eel hydra is a monster that lurks in the murky depths of the ocean, attacking its prey from ambush. It is thought that the eel hydra is an offshoot of the standard hydra that adapted to life underwater, to the point that an eel hydra can no longer live on land and must return to the water periodically to breathe. Much like a land-based hydra, an eel hydra can regrow lost heads, though the eel hydra also generates electricity within its body that it can use to deliver a deadly shock to its prey or potential predators.