Milk Ghost

The Ghost from "James Baxter the Horse" is a character that died prior to the said episode. In the episode, some of the people he knew in his life are attending his funeral. Finn and Jake try to cheer them up several times, with each time the ghost becoming more and more angry. With the final attempt being succesful, he breaks free of his prison and attacks them. However, James Baxter arrives and cheers him up, leaving Finn and Jake alone.

Appearance
At first, he was inside his old body, which was already turned into a skeleton. When he freed himself, he was an enormous ghost.