He was introduced during a fight with Doomguy. Doomguy kept shooting bullets, and they all failed. Shrek won the battle, and did a victory dance. Then it turns out it was just his imagination. He called Doomguy over to try a special onion. Doomguy was actually mad about. Even worse, Mario randomly took the onion and ate it. Doomguy's way to get rid of his anger, was to destroy an onion. He is addicted to onions, that even Stanley Jones said to marry one.