She appears in "The Creeps" when Finn thinks he's the last one "alive," and hides in a room in the Castle. Suddenly the Ghost Lady appears through the wall, and she gazes at Finn while her hair slowly fills the room. Finn then breaks through the wall to the next room to escape (which had a chair and floorboarding that also attacked him). He later finds out the party was just a prank by Jake, but when he mentions the encounter Jake is puzzled, and says that Finn must have imagined it. Later while leaving the castle he decides to forget the experience by putting it "in the vault."
She made a reappearance in "King Worm" when Finn unleashed his subconscious fears to escape his dream. This reveals that although Finn put the memory of her "in the vault" he is still subconsciously afraid of the specter.
In "Sky Witch", Princess Bubblegum passes what seems to be a painting or picture of the Ghost Lady in Maja's house.
In "The Vault" Finn Has a dream about Shoko. He opens the vault to find out that it was his past life. She was under the employ of the Bath Boy Gang to steal Princess Bubblegum's amulet. But before she could steal it, she fell into a river of toxic waste and turned into the creature that Finn saw. She's able to crawl to Finn's future tree house before dying and being reincarnated into Finn.
Shoko was mutilated and abandoned by her parents at a young age which resulted in her taking the path as a common criminal. She only has one arm because her parents sold her right arm for a laptop before dropping her at a dojo to increase her fighting skills promising to return. However, Shoko's parents never came back which has caused many conflicting emotions for Shoko.
Shoko seems to be very responsible for her age but due to her Parent's neglect she decided to live the life of a thief. Even though Shoko commits evil deeds she still feels guilty for the problems she causes which is shown when she cries as she struggles to fight her emotions so she can steal Princess Bubblegum's amulet.
The Ghost Lady has light greyish-blue skin with scale-like lumps and long, green seaweed-like hair. Her neck is unusually long. Her scales are light blue, her irises are black, and her pupils shine red. Interestingly, her appearance differs from the most of the other Ghosts in the series, who are all less colorful and more smoothly shaped. Her design is also similar to a Japanese style ghost. In the castle, just before the top floor, there is a picture of a blue-ish green woman with long orange hair hugging a mutant bull. Whether when woman in the pictures is the ghost in life is remains to be seen.
The Ghost Lady phased through a wall, which was preceded by a ripple effect on the space and a humming sound. Her green hair grew to fill the library that Finn was hiding in, as if trying to reach him. She also may have been able to tear holes through the floorboarding, move a chair, and summon crows from a painting while either offscreen or invisible, but it is possible that other ghosts in the house could have been responsible.