Update, 5/20: Master voice-copier Christina Aguilera struck again on Tuesday, releasing a digital short for her singing-competition show in which *all* she does is impersonate other famous musicians. There's her twerk-tastic Miley, her blind and mute Sia, her long-winded, SAT-word-using Shakira, and, of course, her "Hey, y'all. Join Team Britney. It'll be super fun. Join team Britney, bitch!" Watch the video here.
Original post, 2/24: Further proof Jimmy Fallon rigs the games on his show for his (and fine—the audience's) entertainment: Christina Aguilera sang "This Little Piggy" in Britney Spears's voice Monday night, and it was a random mishmash of things that turned out all right in the end. To quote Jimmy as he giggled delightfully while giving Christina a standing ovation: "Oh my God. That was something I've always wanted. That was amazing!"
Also on Jimmy's very specific wish list: Christina doing an impression of Cher belting out the Folgers Coffee jingle and Christina doing an impression of Shakira belting out the Golden Girls theme song. All three of his wishes were fulfilled in one guest appearance, so watch the video below.