Losing your head
Johnny Cage's uppercut decapitation fatality in MK2 could be converted into a triple decapitation, punching three heads off one defeated enemy.
Mortal Kombat Mythologies: Sub Zero was a platform adventure based around the controls for the main MK games, so you had to push up on the D-pad to jump. Planned follow-ups did not appear.
Christoper Lambert appeared as Raiden in the successful movie adaptation of Mortal Kombat. Raiden was generally spelled Rayden in home console versions.
Comedy of errors
When the word ERMAC was spotted in the original game, players thought it was a secret hidden character. In fact it was just an errant programmer debug message that stood for "error macro." Ermac was added as a character in Ultimate MK3.