New Super Mario Bros. 2 [3DS]

Limitless 1 ups
Visit Mushroom World course One, where the 1st star coin is. Get up on top of the stairs and then wait for a noko noko. Move lower to the 2nd or the third step and wait for an noko noko to contact you. Jump on that lightly (not hitting jump once you hit it) and after that it will bounce off the wall and Mario will continue jumping on it, helping you to obtain Three crowns during first minutes.

Unlock Luigi
If you wanna play as Luigi in single player mode, you should very first complete this game by defeating Bowser in World Six. Once you do this, when in the file select screen, keep down the L plus R buttons while choosing a file with the A button. Luigi will now become your selected character.

Limitless Mushroom Houses
For this you need to Clear the Star World.

Unlock 2nd Title Screen
If you collect 1 million coins, you will unlock the second title screen with more coins and gold mario.