The Ghost Lady appears in "The Creeps" when Finn is the last one "alive" and hides in a room in the Castle. The Ghost Lady appears through bookshelves, and Finn breaks through the wall to the next room to escape. Everything in the party was a prank except for the Ghost Lady, and chairs and floorboards trying to attack Finn, which Jake had no idea about when Finn asked him if he had set those up as well.
The Ghost Lady has light greyish-blue skin with scale-like lumps and long, green seaweed-like hair. Her neck is unusually long. The whites of her eyes are light blue, her irises black, and her pupils shine red.
The ghost lady phased through a wall, her approach heralded by a ripple effect on the space and a thrumming sound. Her green hair grew to fill the library that Finn was hiding in, as if trying to reach him. She was able to tear holes through board flooring, move a chair and summon crows from a painting while either offscreen or invisible.
- In the castle's foyer, there is a painting of a long-orange-haired, blue-skinned, purple dressed lady hugging a bull. This is possibly a painting of the Ghost Lady in life.
- Based on her "scales" and long seaweed like hair, Ghost Lady may be some type of Siren or a "water witch"