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.
Carroll appears again at the end of "Come Along With Me" as a Water Nymph. She can be seen drawing at the edge of a body of water in The Grotto with the ponytail Water Nymph behind her.
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 the blue skin and flowing water hair as the other nymphs, but she wears a black one piece swim suit.