Wario Land 2: Nusumareta Zaihou

Beat the game with 100% treasures and map pieces. Along with an extra level, you will also get a mini game: Flagman D.D.

This glitch allows you to slide the wrong way up a hill. Position yourself about 3 or 4 steps from the top of the hill. Body Slam (B Button) up the hill. At the top, press Down. If done correctly, Wario will roll away from the top of the hill, going up the hill.

To access a secret level and new ending, instead of waking up Wario to begin the game, let him continue to sleep. Level 1 will come to an end, pirates will carry Wario out to the nearby woods where the level begins.

When you get to the door that enters in to the bunny boss, simply pick up the little swordsman that is on the other side of the room and throw him(full strength) against the wall above the door, go through the hole in the wall you just made, pick up the swordsman again and throw him into the next wall, go through that hole and there is the secret exit.

Anytime during the game, you can hold down Start and Select then press A and B simultaneously. This will reset the game back to the title screen.