Katy Perry falls out of her chair on 'American Idol' while dressed as the 'Little Mermaid'

Legs are required for jumping and dancing, and Katy Perry learned that the hard way during last night's live broadcast of American Idol. As she's done for previous Disney Nights on the show, Perry went all out with her costume, dressing up as Ariel from The Little Mermaid in a cosplay that would make …