Blood Jelly (5e Creature)
From D&D Wiki
Small monstrosity, lawful evil
Hold Breath. While out of water, the blood jelly can hold its breath for 1 hour.
Water Breathing. The blood jelly can breathe only underwater.
Electrify (Recharge 5-6). If the blood jelly is in water, each creature within 10 feet of it which is also in water must make a DC 14 Constitution saving throw, taking 16 (3d10) lightning damage and becoming stunned for 1 minute on a failed save, or taking half as much damage and not being stunned on a success. A creature can repeat this throw at the end of each of its turns, ending the effect on itself on a success.
Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 11 (2d8 + 2) bludgeoning damage.
Microscopic, blood-born parasite swimming in the bloody waters of the Crimson become themselves infected, converting them to its all-consuming cause. A blood jelly is a dense ball of muscle and bone with only superficial resemblance to a jellyfish. They are capable of launching themselves at surprising speeds and releasing powerful surges of electricity.