Zombie
In another dimension, there was once a great tree spirit whose tree grew so large that its roots began to suck up the very life force of the world. The entire biosphere became bound to this tree spirit, called Nexicul, becoming soulless zombies controlled by him.
Nexicul seeks to expand his influence into other worlds, including Otter Island. Because Nexicul is fae, he cannot go where he is not invited, so he cannot take Otter Island directly. What he can do is find some fool in one of his various dimensions who is willing to take one of his zombies where he wants them to go.