On Mt. Rugged, when you encounter the Buzzard enemy, tell it that your name is Luigi, and you won't have to fight it.
Avoid using FP
If you can pull off a FP-consuming attack outside of battle (Such as a Spin Jump) and get a First Strike, you will automatically use that attack in battle without using any FP. This also works for Mario's partners' attacks.
Free unlimited hearts
While in toad town, from the post office head to the right. Eventualy you will see 3 blue creatures. The one on the left moves its eyes, and the other two dont. Walk in circles around the one with moving eyes to recive more and more hearts!
Luigi's Secret Basement
First, get the Super Boots. Then, go to Mario's house via Toad Town and stomp the ground inside Mario and Luigi's bedroom. Eventually, you'll see a tile on the floor going up when you stomp. Stomp on that tile and the floor will bust open Luigi's secret basement, and inside is his own secret diary!
Original Mario music
When a new chapter begins, wait a little while and the original ''Super Mario Bros.'' music will play.
Original NES Mario
In Boo Mansion, go through the door across the hall from the entance, the one with a large jar in it. Jump in the jar and NES Mario pops out! Leave the room or jump back in to change back.
Shocked Luigi
To give Luigi a real scare, exit Boo's Mansion BEFORE getting Lady Bow. Return to Toad Town (You still have to fight Jr. Troopa, darn it), jump into your Pipe, and return home. Enter Mario's room and look for a strange-looking part of the floorboards (Entrance to Luigi's Diary). Go through and Luigi will be writing in his diary. He sees you, becoming stunned for a moment, then fleeing. For fun only. Does NOT affect storyline or Luigi's Diary entries.
Unlimited levelling up and easy exp
Normally all enemies stop giving you star points when you pass a certain level and you\'re forced to visit a new area to be able to build any levels. However, there is one hidden enemy in the game you can fight repeatedly regardless of your level and will give you over 40 star points, the equivalent of fighting 40 easy enemies.
In the flower fields, take the bottom right hand path and cross the spikes with lakilister. A glowing amayzee dayzee will randomly appear with 1/4 odds. It may run away, so try a dizzy spin attack to daze it before the battle starts and kill it in two turns for massive star points. Travel two screens away and repeat the battle to hit the max level easily.