If you save and quit while you were playing in any of the special worlds, the next time you go to the home screen there will be alternate video! (Note: this can be reversed by saving and quitting in any of the first 8 worlds)
Get a Tanooki leaf.Play level 7-1.When the level starts, run towards the flag.When you come to the pit with the water, jump and hover over it.If you do this you can hit the flag and beat the level in 5 seconds, or less.
In world 1-2 there is a classic Mario throwback. After the checkpoint flag you'll see some coin blocks. If you jump on top of these you can then jump further up and away from the screen. You'll land on a small narrow ledge that you couldn't see before. You can now run past this section of the level and when you come to a gap in the higher area jump over it and keep running, you'll come to an area with a single orange pipe. Jumping in this pipe will take you to World 2.
When viewing a photograph, as with the photo album, shake the 3DS to put some objects and characters in motion. For example, shake the 3DS when viewing the photo from World 4. You will eventually see Luigi jump up from the behind the castle wall in the background.