Karush

Karush, known as the Archdruid of Decay, was a member of the Pact of Iron, and one of the seven rulers of Orioth during the Age of Iron. He ruled Cape Savorel. A powerful druid, he was drawn to death and decay, and saw entropy as the most beautiful aspect of life. Seeking immortality, he commited a profeane ritual in the heart of the Odium Bog, at his seat of power known as the Withered Grove. In this ritual, he drew dark magic of Decay to himself, and allowed himself to die, and bedevoured by the various creatures of the Bog. The power of the ritual set his soul free, allowing him to posess the bodies of the creatures of the swamp.
Any time he posessed a creature, such as a snapping turtle, gator, or catfish, the body would twist and mutate into a bipedal monstrosity, a heinous, corrupted form based on the posessed beast. If the body died, he simply jumped to the next one. The Order of the Golden Rose managed to slay him at the end of the Age of Iron, by embedding a gem enchanted with a SOul Anchor in the body of a gator, and tricking him into posessing the sealed body, stopping him from jumping again.