Also, I've found a glitch that gives Mario/Luigi a VISOR-looking black thing over their eyes! It works in the Advance version, but I'm not sure about the SNES version.
1. Go to Star World 1.
2. Go to where he key is.
3. Pick the key up.
4. Walk all of the way to the right, so the key is in the wall.
5. Release the key.
6. Now, your character will look weird! You can move out of it, so it doesn't have any lasting effect, but it's cool!
It''''s funny until someone gets hurt. Then it gets hilarious!