Alternate-Universe Patrick appears in the episodes "Roller Cowards" and "Rule of Dumb." In "Roller Cowards," AU-Patrick called Patrick a "big fat crybaby." Patrick responded by punching him and saying 'I thought we settled this the last time!", implying that he and Patrick encountered each-other before. In "Rule of Dumb," AU-Patrick looks like Patrick, but with a unibrow, spines on his hunchback, a nose, and large pointed bottom teeth. Patrick and AU-Patrick can only see each other using a mirror. They can reach into each other’s worlds (proven by Patrick, when he punches AU-Patrick.) Patrick and AU-Patrick don't like each other very much. He also appeared in "The Great Patty Caper" when Patrick suggests that his reflection in the window looks suspicious. Afterwards, the reflection gains a smug expression, then walks away.
His most recent appearance was in a unnamed SpongeBob comic in the Nick MagazineSeptember2009 issue. In the comic, SpongeBob and Patrick receive a treasure map from an elderly sailor. SpongeBob reminds Patrick of the curse that the sailor told them off. When SpongeBob then tells him about what the sailor said, a bubble comes up with Alternate-Universe SpongeBob, Alternate-Universe Patrick and Alternate-Universe Elderly Sailor reenacting when the sailor giving the map to them. When Patrick denies that even happened, the Alternate-Universe Sailor slaps him and says "Sure I did! Pay attention, sonny!" Then, in the background, Alternate-Universe Patrick is laughing at him and Alternate-Universe SpongeBob is staring at SpongeBob with a blank expression.
"I am you and you are ME!!!"
"(Both Patrick and Mirror Monster) AH! WHAT HAVE I BECOME!?"
"You! I don't get it"
Unlike Alternate-Universe SpongeBob, Alternate-Universe Patrick is always shown to be evil as he tells Patrick that he is a crybaby and even laughs at him when he gets smacked by the Alternate-Universe Sailor.
The Mirror Monster might be based off an old theory on how the mirror world is actually filled with dark energy such as monsters.