Spot the Diff, or Change-inator-inator, is the name given to a special two-hour Phineas and Ferb mini-marathon, first aired on Disney Channel US in 2008. The marathon is based around a scenario in which Dr. Doofenshmirtz has made an invention he calls the Change-inator-inator, with which he can make various changes, particularly visual ones, to certain episodes of the show. The changes are shown through specially-made promotional spots airing between each episode, with redubbed animation from "The Fast and the Phineas". As a challenge, the viewer watches the four selected episodes and their modified counterparts while keeping track of which changes are made as part of a tie-in at the official websites.