Enter a level with Yoshi, Cape Mario, and a Fire Flower in reserve. Position yourself under a berry in a way that you can get the fire flower and get the berry at the same time. If you happen to eat the flower and the berry at the same time, the game will freeze. Several things have been reported while using this glitch. Sometimes when the game freezes, your coin count will rise until you quickly have 99 lives. Press Start and Select to exit the leve. One person's game froze, horizontal lines appeared on the screen, and weird music kept looping over and over again. Then came a buzzing noise, and he was returned to the file select screen, with his file deleted. Thankfully, that's not normal. Even so, this is an interesting glitch to exploit every once in a while.
In the "Special Zone", wait about 5 minutes and listen to the music. It should start playing variations of the original Mario Bros. song!
Complete Any Level Instantly
For this glitch, you'll need to get Fire Mario and Yoshi in Yoshi's Island 2. Near the end of the level, there is a Piranha Plant in a pipe near a Dragon Coin. Stand on said pipe, about 2/3 of the way across. Pay attention to the Rexor to the right. When he is walking left and about 3/4 past the Dragon Coin, crouch, then press X+A simultaneously. Mario will jump off of Yoshi as Yoshi attempts to eat him, and you'll get some weird glitchy item in your item storage. (If you did it wrong, the game just crashes horrifically.) If you summon this item during a level, and then grab it, the level is then completed, provided that Mario does not die while attempting to walk off-screen. Note that the orb only works once, and you need to get it again to complete another level.
Death Cancel Glitch and Infinite Time
When your timer is about to reach zero, pick up a power-up at the same time as the timer reaches zero. You will hear the sound for when Mario loses a life, but he should not die, and should still be permitted to move around. The timer will remain at zero until Mario dies or the level is completed.
Easy Extra Life
Beat a stage with your time ending in the same digit repeated twice as the tens place of your Star total, and you'll be awarded an extra life. Example: With seventeen stars, beat the stage with your time ending in eleven.
Extra Lives - First Ghost House
In the first ghost house, fly up to the upper left corner. You will see a ledge. Run to the right and you will fall. Ghosts will try to hurt you but keep on going. At the end of the ledge you will fall and there will be four extra guys. You will have to hit the boxes to get them. Go though the door. There will be a Moon (3 lives.) After you beat it there will be a level above the ghost house. Go to it. In it there is five boxes. The two left ones contain, flowers. The two right ones contain feathers. The middle one has Yoshi. If you already have Yoshi then it will be an extra life. To exit, run off the screen.
Extra Lives - Forest of Illusion 1
For a total of fourteen lives do this. Go to forest of illusions 1 and get to the half-way mark and then keep going untill you see a box with changing powerups. Now wait until you see a feather in the box. Then hit it and it should change into a star. If you get the star, run and kill all the creatures that come out of the yellow blocks untill you start getting lives. The turtles and other guys are worth one life and the wigglers are worth two lives. You can get 99 lives much faster this way.
Extra Lives - Vanilla Secret 2
Enter Vanilla Secret 2 and get to the half-way mark without killing any Koopa Troopers or the green jumping guys. Keep on going until you reach a pit with a lot of spinny orange guys. There will be yellow blocks right above the pit. Hit the blocks until you get a silver "P" switch.
Carry this switch a little past the half way mark until you reach two pipes with red guys jumping out of them. Put down the "P" switch, step on it, and run back to the start of the level. While your running there will be a lot of silver coins on the way. Get all the silver coins you can and you will gain 50+ lives!
Important: Be sure not to kill the Koopa Troopers (or the green junping guys) on the way to the "P" swich, those guys turn into the coins that give you the lives.