|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.
Fisho the Colossal is the dungeon boss of Ice King's Hall of Just Ice. She is giant fish monster with a one giant eye, three mouths and a chain-saw on her back. She is killed when Finn eviscerated her and Ice King ripped off her chain-saw, which caused her to explode. She was created by Ice King to guard his treasure, which was a picture of him and Betty.