Imposter's Home for Um...Make 'Em Up Pals

S3 E4: 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 his real identity.