Display the credits, then select the text "IM IN UR CONSOLZ DFENDIN UR CASLEZ" when it appears.
Easy way to pass levels
During a level, press Pause (+). While you are paused, the in-game clock keeps ticking, meaning the sun keeps moving. After the sun is gone for a little while, un-pause and you will have beaten the level.
Giant stick figure mode
Press ''SMB3W4'' during the credits.
Pause Exploit
Pause the game and the sun will still set. Unpause the game when it is night and you will beat the level without lifting a finger.
Small stickmen
Display the credits, then select the text "Chuck Norris" when it appears.