The Lemon Chef is the name of a character who first appeared in "Just Set Up the Chairs".
Skips created him from pieces of the games "Hats 4 Sale", "Lemonade Stand","Ball of Yarn", "Candle Maker", "Deli Dude" and possibly "Staring Contest". Lemon Chef was piloted by Mordecai, Rigby, and Skips to defeat the Destroyer of Worlds by shooting hamburgers from his hands. Once the Destroyer was defeated, a cherry power-up appeared, and the Chef obtained it.
Lemon Chef destroyed the Destroyer of Worlds once more in "Exit 9B".