Misty is a character from Pokémon. She dresses up as a mermaid in Season 1, Episode 61, called "The Misty Mermaid".
Misty is roped into a underwater ballet by her three sisters, Misty played the mermaid part. The first part of the ballet went well, but the second part was interrupted by Team Rocket, who took the place of the villains in the story, and tried to capture water pokemon. Misty held them back and fought them off along with Ash and Brock. Despite all this the audience thought it was all part of the act and loved the show.