The Friendly Ghost (1945)
Michelle mentions getting a tattoo of the title character
Dave Sacks is credited as "Dave 'The Friendly Ghost' Sacks."
In "Spooking Bee", Casper morphs into the 1945 version of himself as means of coming up with a good scare.
Phineas is singing Casper's theme in one scene of "Casper vs. the Ultimate Fanboy."
Episode name "Squidward the Unfriendly Ghost" references this short's name.
Episode title is named G-G-G-Ghost Dad! after the movie Ghost Dad. The "G-G-G-Ghost" part is based on what everyone who ever saw Casper shouted in this cartoon.
Title mentioned during Kevin Connolly interview
Casper is mentioned
Luke Parker asks Liv Parker, "how was I supposed to know that Casper the English ghost would be a complication?"
Mitch's suggestion as to what start the six way skype call during their intimate conversation.
Zapp Brannigan watches it on a projector.