Bart vs. the Space Mutants Cheats (Nes)

The first ashtray past the escalator in the mall is the entrance to a secret room full of
hats.

If you enter the theater on the first level between 2:00 and 4:00, you will enter a bonus
room. It may
  take a few tries.

After you buy a whistle at the store, go to Grandpa Simpson's nursing home and use it.
Wait awhile
  and Grandpa Simpson should start tossing you coins.

In Level 1, stand to the right of the "E" in the "Quick-E-Mart" sign. Shoot a rocket at
the "E" to make
  a Krusty Clown Face appear that gives you three 1-Up's and a Sound Test. For the Sound
Test,
  select it and press Start. Select sounds by pressing Up/Down, then press Start.

If you fire a Rocket at the E in Kwik-E-Mart a 1 up flies down.

Buy the magnet from Toys N' Stuff on Level 1. Use the magnet on the wheel game on Level 3.
Pick
  any number while using the magnet, and the magnet will draw the wheel toward your
number. Instant
  win!

To get a bonus in the first level, go to the theatre at two or four oíclock. Wait at
the entrance for the
  boy in purple to exit and spray him!