In the final episode, titled "The Graduation", Mork from Ork makes a brief appearance, commenting on the bittersweet nature of the occasion. He says to Orson Welles (who plays himself in the episode), "Those were sad days, weren't they?" to which Orson replies, "Yeah, they were."
This cameo was a nod to the popular sitcom "Mork & Mindy", which was also created by Garry Marshall, who also created "Happy Days".