[aaroninsf]

My favorite easter egg by far in this domain, was the Apple II version of Karateka.

The game came on a floppy disk; if you inserted it in the drive upside down (the Apple II only used one side of the medium) you found (unusually) that the game would load, but was rendered upside down.

It was fully playable. Non trivial given the way those games were written!!!

[msephton]

This is mentioned in the Karnataka history. Apparently it was trivial to implement and discovered somewhat by accident. https://www.gamedeveloper.com/game-platforms/-i-prince-of-pe...