Rex is an enemy in the Mario series whom first appeared in the game Super Mario World. In the game, it would take two stomps until they would be defeated. Once Mario stomps on them once, they would become smaller, though they would start to run faster. Rexes later appear in the game Mario & Luigi: Superstar Saga where he would appear on Hoohoo Mountain, just like in Super Mario World, he would become flattened/smaller if Mario or Luigi jumps on them. The enemy later appeared in Super Princess Peach where Peach must defeat them by jumping on them twice.