Extra Toad Houses

At the end of the levels, jump onto the flagpole and when the last two digits of your countdown timer are the same. For Red Houses, jump on at 11, 22, or 33. For Green Houses, jump on at 44, 55, or 66. And for Orange Houses, jump on at 77, 88, or 99.

Inifinte 1UPs

At the pipe right at the end of World 1-4, kick a shell and it'll keep sliding back and forth between the pipe to the right and the wall to the left. If you jump every time the shell comes your way, the shell will kill the enemies that constantly appear, eventually giving you 1UPs

Item Gauging

To get a particular item from the red mushroom houses then hop into one.when toadsworth starts the slot go under it. Here's the tricky part: pause the game two items before the one you want and double tap A or B. For example, if you want a mini mushroom pause the game at the flower and press A or B twice. Ta Da! you got the mini mushroom.

Play as Luigi

Beat the game and save it. Then, select the saved game and hold down both the L and R buttons, then enter A. Then Luigi should be unlocked to play as.

Warp to World 5

There's a warp pipe that'll instantly bring you to World 5 from the World 1-Tower. When in the hidden room with the second Star Coin, notice a small gap in the upper-right corner of the room that's never closed by the shifting blocks. You can jump into the gap to reach a hidden area with a 1-Up (smash the invisible blocks as soon as you enter the room). Shell Mario can go one further, breaking the blocks along the floor to reach the warp cannon