|The following information is from the Adventure Time comic book series.|
It may not be part of the same canon or continuity as the animated series.
Fart Fairies are a species of fairy that appear in Laundromarceline. Marceline asks Finn and Jake to clean them out of her chimney in exchange for drinking the red out of their laundry. They start to fart when they fall out of the chimney, and Finn and Jake run away.
Fart Fairies are tiny creatures that have two legs but no arms. They come in a variety of colors, and have a set of wings on their backs. As their name suggests, they fart constantly.