Bart Simpson has to stay up late and write a paper for class tomorrow. For once, he is determined to get a good mark. However, very quickly, he falls asleep. Nightmare after nightmare haunt his subconsciousness, and it is up to you to get over each one, so that Bart will eventually wake up.
Bart's Nightmare is an action game based on the TV cartoon show The Simpsons. The player navigates Bart through the side-scrolling overworld, collecting pages of his homework while avoiding various enemies modeled after characters from the show. For example, his sister Lisa would occasionally turn him into a frog, Principal Skinner may force him to wear a Sunday school uniform (slowing his movement), etc. Bart can repel enemies by blowing a bubble gum at them.
Once a homework page has been found, the player can step through colored doors and engage in various mini-games. These involve Bart transforming into a "Bartzilla", a giant monster out to destroy Springfield; swimming through Bart's own bloodstream, using air pumps to kill germs; being attacked by Itchy and Scratchy, the duo from the meta-fictional violent cartoon; flying over the city as the superhero Bartman, fighting boss enemies; and exploring the treacherous columns in the Temple of Maggie as Indiana Bart.