Gary the Mermaid Queen appears in the episode "The Witch's Garden" as an antagonist. She is a skeleton that resembles a ghost or harpy more than a traditional mermaid—probably justified by the fact that she lives in the River of Junk. Nontraditional in appearance, she customarily tries to mate with the males that she finds. Her bony hands are somehow connected to her hair, which she can easily move in a circle around her body. Gary is first seen when Finn, while looking for objects to make a catapult, takes a trash can lid off her eye. She is later seen outside and asks, "Which one of you mortals wants to mate with all this?" According to Finn, she is "the grossest thing ever," which angers Gary, who then attempts to feed Finn to her supposed Hatchlings. Jake soon regains his powers and saves Finn, sending Gary back into the river.
Gary seems to be a floating mermaid made of bone. Her hands are connected to her hair. She has gigantic white eyes and hair that resembles Marceline's, and a long, slithery tongue. Finn describes her as ugly.
Gary can float, spit black, and create blue flames from her hands.
Behold, the beautiful mermaid of the river! Which one of you mortals wants to mate with all this?
Remember to save the brain for dessert!
- Gary's hatchlings do not resemble her; instead, they look like baby birds or chicks.
- This may be because, instead of being a mermaid, she may be a siren. A siren is a half bird, half human Greek mythological creature. Sirens sometimes vary in forms, such as half fish or full woman body, making recognition a bit difficult.
- Gary does not really resemble a mermaid.
- This is further disputed, as she has legs instead of fins.
- This means that she is possibly a Siren.
- Her saying "Which one of you mortals wants to mate with all this?" was censored.
- The Goblin King finds a mermaid girlfriend, and supposedly, Gary is still the ruler of the mermaid even though the two look nothing alike.