Booboo is a ghost that appears in "Heat Signature." He is a ghost with two heads. He helps Marceline prank Finn and Jake but, just like his fellow ghosts, takes it too far. Likewise, he is portrayed as being cruel and mean. He seems to have had a spot in Marceline's former gang from the underworld.
Booboo has the stereotypical body of a ghost, a pale, semi-transparent blue. However, Booboo has two heads, each of which speaks independently. Booboo can also suck a living being's guts out through their brains.