Each-Uisge
Each-uisce, cabbyl-ushtey, elder kelpie; CR 7
Home plane: Feywild
Alignment: LE or NE
The older, darker, and more dangerous cousins of kelpies, the each-uisge (eck-OOSH-kya) prefers seas to lakes and rivers. They are fey creatures whose true forms are monstrous shape-shifting heaps of rotting plant matter and soaked peat. Like kelpies, each-uisge are intelligent ambush-hunters, who take the shape of humans or horses. However, they are much more versatile in their shape-shifting powers and more dangerously intelligent.
COMBAT: Each-uisge are powerful foes in direct combat. They have sharp teeth and powerful hooves, along with vine-like tentacles. However, they still prefer to use charm and deception to hunt. Each-uisge can take the shape of a humanoid, equine (both mundane and magical like hippocampi), cattle, seal and even large bird (although they can’t fly—so they prefer to appear wounded or mimic flightless birds like great auks and penguins). They are supernaturally charming and can convincingly entice a berk to enter water with them. At that point their hide suddenly becomes extremely sticky, and the each-uisge strikes, dragging its prey down under the water. This tactic is the most prevalent among these dark fey, but it isn’t the only one they use. Each-uisge are cunning, and purposefully spread misinformation about their kind (such as the famous myth that kelpies can be somehow tamed).
HABITAT/SOCIETY: Each-uisge typically avoid one another. They don’t need to breed and two only get in each other’s way. However, each-uisge have another important ability—they can magically dominate kelpies and other plant monsters like shambling mounds. Locations where freshwater springs and saltwater seas meet each other are the most dangerous, as each-uisge in those areas often have a number of kelpies at their beck and call.
ECOLOGY: Each-uisge mainly feed on humanoid meat, although they can go for a long time without any food, being partially sustained by sunlight. They build simple lairs in the underwater caves or seaweed forests, where they hibernate during winter. Often, these lairs have some treasure, including magic items, though each-uisge are rarely able to use any of them.
Source: Margarita. The each-uisge is homebrew, based on the monster from Scottish folklore.