The Monster Cookie appears in a dream of Cookie Monster's in a Sesame Street sketch, a personification of the phrase "You are what you eat." After Cookie Monster finishes some birthday cookies his grandma gave him, there are none left for the birthday party. When Cookie Monster takes a nap, he dreams of meeting the Monster Cookie.
The cookie tells the sad tale of how he became that way -- He was once a regular fuzzy monster also, but eating only cookies every day caused him to turn into a cookie. Now, he regrets not eating healthier food. When Cookie wakes up after his dream and takes his vision's advice and vows to never eat cookies again. He eats some healthier food (such as carrots, fish and whole-wheat bread), but eats a cookie afterward, commenting "Maybe sometimes a cookie."