She was on the Simpsons in "The Fight Before Christmas" where she played herself.
In this special, she is Moe's sexy girlfriend and appears after Mr. Burns enters the Simpsons' home. She believes that the house (which the Simpsons told Moe to care of) is really a bachelor pad. She also seduces Mr. Burns by kissing and squeezing him in her exposed cleavage. She along with all the characters (as puppets) begin to sing "The 39 days of Christmas".
After the credits, She is last seen with Moe who is trying to kiss her, but is unable due to his height. He then decides to kiss her belly button, but is really kissing her vulva. A surprised Katy Perry reveals this to him and stops, but tells him to continue and continues kissing her vagina, much to her delight.
Katy wears a red latex embordered with simpsons faces and a low cut top which reveals her exposed cleavage.
Katy is shown to be very flirtatious and likes to motorboat people, such as when she motorboats Mr Burns in her cleavage and starts kissing him.