Invincibility
Type cowabunga and press [Enter] at the title screen.
Level 1: People to spray
There is a difficult item to find on the streets. Near the start you can see a phone box. Enter it and call Moe's Tavern (opposite). He will appear wearing a purple "dress". When Bart tells him a joke, he takes a psyke and dives at you. Spray him, then jump. At exactly 4:00, some purple wearing people will leave the theater. Spray them. There is a man near the statue of Jebidiah Springfield to spray.
Level 1: Extra lives
Locate the invisible platform in the first level that is right next to the first store, about three inches away from the building to the left. It may be difficult to find, but will result in some letters coming down and two extra lives.
Shoot rockets at the "E" in the Quick E Mart for some extra lives. Rockets are bought at the Toy Store.
Level 3: Five coins
Reach the big Krusty head in level 3 (Krustyland). Jump on the red platform in between its eyes. Then, jump down to grab the extra life. Keep jumping straight up to enter a room that contains five coins.
Level 3: Winning the wheel game
Purchase the magnet from Toys N' Stuff store on level 1. When playing the wheel game on level 3, use the magnet while selecting a number. The magnet will allow that number to be selected by the wheel.
Bonus screen
Enter the theater between 2:00 and 4:00.
Extra coins
Purchase the whistle from the Toys 'n' Stuff store and go to the nursing home. Blow the whistle and wait for Grandpa Simpson to begin throwing coins.
Location of the heads
On level one, buy a cherry bomb. Go to the pet shop, get above the window, and shoot it at the bird. Then, when you get to the Statue of Jebediah Springfield, get on the second line in back of the statue and shoot the bird with a rocket. This will provide the head of the statue, which will make Bart invincible for a short period of time. However, the heads are found in secret places on various levels. On level 2, reach the shoe level. When the first ballet shoes appear, keep jumping on that ashtray to collect coins, hats. Keep jumping to receive the head of the statue. Also on level 2, find the location where there is wet cement on the magic board. Between the fourth or fifth wand, jump as high as possible from the fourth to fifth wands. The head will appear on the fourth wand. On level 3, there is a big ladder that Bart climbs. Hit the kid at the top with the sling shot. Move all the way to the top of the ladder, and jump off. Land right on the board to receive three coins and the head from the statue from the prize section just left of the ladder.
Extra money
Obtain the whistle, then stand next to the last window at the Springfield Retirement Home. Blow the whistle to collect money from a man that appears at this location.