Carroll is a Water Elemental that Finn encounters in the episode "The Tower." She used to be a body of water, but after growing tired of people swimming in her, she evaporated. She at first mistakes Finn for one such swimmer, calling him a "real swim nut" after face-blasting him with her lightning gun. Carroll becomes nicer to Finn once she finds out he is having problems and is not a swimmer, and even offers him some advice. She lives in a cloud house that can be flown around.
As a Cloud Person, Carroll is a puffy, small, and has stubby limbs. She has cloud 'hair' that covers her left eye. As an Ice Person, she is made out of a solid angular block of ice. When she is shown as a Water Nymph, she has blue skin and flowing water hair like the other nymphs, but she wears a black one-piece swimsuit. She also appears to be smaller in stature than the other nymphs.
- "The Tower" (debut)
- Carroll takes on a different form in each of her appearances, though she always has her "hair" combed over one eye. The three forms represent different stages of the water cycle, including gas/vapor (her cloud form), solid (her ice form) and liquid (her pond and Water Nymph forms).
- In her last appearance, she is drawing a picture of a woman with a bow and arrow and pointed ears, referencing her remark in "Winter Light " that she draws elves. This elf drawing is seen inside BMO's home as "King of Ooo."