Wraiths

"After many years of ceaseless research and dedication, the mages of Estelore finally succeeded in opening a portal of their own. A portal which, they soon learned, had no destination. It went to a space between worlds: an endless void. From this void came creatures, beings of formless entropy and otherworldly vacuity that inhabited that plane of nothingness. They slipped through the portal in the moments it existed and, being creatures of spirit rather than flesh, possessed the archmages of Estelore. Not a week passed before all on the island were under the creatures' dominion." – Corruption of Champions II: Public Design Document

Wraiths are creatures of the realms between, and can enter mortal realms mostly by incautious use of portals. They dont feel anything, and their driving force is seeking out other creatures to devour their emotions, feelings, and the likes. If a wraith eats entities with sufficently strong feelings/emotions/etc, they might turn into... Something else