Wendy is a ghost that first appears in the episode "Heat Signature." She, with Booboo and Georgy, are friends of Marceline. The three help Marceline prank Finn and Jake into believing they have been turned into vampires. The ghosts and Marceline make Finn and Jake believe they are invisible, and accidentally upset Lumpy Space Princess' tin of beans in the woods. The ghosts begin to take the prank too far, and start beating Finn and Jake up. The ghosts take them to the top of a high building and tell them they will be able to fly as they are now vampires. Finn and Jake jump, and Marceline saves them just before they hit the ground. Afterward, they lure Finn and Jake back to their house behind Marceline's back and try to suck their guts through their heads. This shows that the ghosts are cold and have a dark type of humor, almost like Marceline, except they don't know when to stop. Their lack of respect for Finn and Jake cause Marceline to be less inclined to be friendly to her former buddies, after she saves the two adventurers.
Wendy, like her fellow ghosts, is a pale blue semitransparent being and looks like her friends only she has breasts. She can grow to extreme sizes and her mouth can grow into a long, anteater-like snout-thing to suck out peoples' guts through their head. When she is sucking out Finn and Jake's guts, she is wearing a bib with lace. Booboo and Georgy wear similar ones when gut-sucking.
Wendy doesn't care about anyone still alive but seems to like the undead. She is a carefree ghost, although temperamental.
Marceline: What are you guys waiting for? You said you had a plan.