Foster's Home for Imaginary Friends

S03:E04 - Imposter's Home for Um . . . Make 'Em Up Pals

When Goofball, a messy, mooching and suspiciously human teenager-looking Imaginary Friend, shows up at the house, he makes Frankie's already lengthy To-Do List even longer. Certain that the Imaginary Friend is an imposter looking to take advantage of Foster's fine amenities, Frankie sets out to prove Goofball's real identity.