Each Uisge (5e Creature)
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Large fey (shapechanger), chaotic evil
Damage Vulnerabilities fire, radiant
Charge. If the Each Uisge moves at least 20 feet toward a target and then hits it with a hooves attack on the same turn, the target takes an extra 4 bludgeoning damage. If the target is a creature, it must succeed on a DC 15 Strength saving throw or be knocked prone.
Shapechanger. The Each Uisge can use it's action to polymorph into a fair horse or pony or back to it's true form. It's statistics, other than it's size, are the same in each from. It reverts to it's true form if it dies.
Sunlight Vulnerability. After each turn the Each Uisge spends in the sunlight, it begins to melt, it's skin blistering and popping. It takes 1d4 radiant damage while in the rays of the sun. Damage taken from the Each Uisge's Sunlight Vulnerability does not regenerate. After being reduced to half it's health in sunlight, it gradually turns transperant and gelatinous, this removes it's resistance to unheated weapons and reduces it's walking speed to 10 ft. as it struggles to keep itself together. If it is dead within the light of the sun, it fully melts into a pile of repulsive gelatin.
Water Regeneration. While the Each Uisge is submerged in water, it regenerates 4 damage by the end of it's turn unless the damage taken was radiant or fire damage.
Adhesive (True Form Only). The Each Uisge adheres to anything riding it. A Large or smaller creature, adhered to the Each Uisge is also grappled by it (escape DC 14). Ability checks made to escape the grapple have disadvantage. The Each Uisge cannot attack any creature riding it.
Multiattack. The Each Uisge makes two attacks: one with it's hooves and one with it's bite.
Hooves. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) bludgeoning damage and 3 (1d6) piercing damage.
Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 4) piercing damage.
The Each Uisge lives in water, generally seas or large lakes. At night, it crawls out to seek prey. It usually preys on humans by transforming into a fair pony or horse that appears to have lost it's way. When a rider mounts it, it reverts to it's true form and adheres to them, preventing escape. It then sprints towards the nearest body of water and plunges in with them still attached. While in the water, it attempts to drown them unless it knows they cannot drown or are rather powerful, in that case, it attacks them. The Each Uisge's slimy skin repels most attacks, but a sword left in a fire to heat can easily penetrate this layer. Though it mostly attacks humanoids, it will consume livestock (of course not by appearing as a horse but rather by rending it to bits). After it's prey is underwater, it rends it to pieces and consumes all of it but the liver, which is both distasteful and poisonous to the Each Uisge and floats to the surface. People who know of Each Uisge and see the horrid sight of the bouyant organ will know that an Each Uisge lives in those waters and recently had a meal.