Go to a door on your left. Use a POW block or "?" and go to the door and get the secret code. This code will give you free mini-games when you go to the level selection screen.
World 4-1: Easy lives
Go up the first steep hill until you get to three pipes and a Koopa walking around. Two will have Piranha plants and one will be a Shy-Guy generator. Throw away an egg so Shy-Guys will start jumping out. Kill the two Piranha plants, eat the Koopa and stand on the pipe. Spit the Koopa shell towards the Shy-Guys. The shell will bounce between the two pipes, knocking out the Shy-Guys. As soon as ten Shy-Guys are knocked out, you will start getting a 1-Up for each consecutive Shy-Guy. The shell will keep bouncing around, killing the Shy-Guys that pop out. You can get up to 999 lives this way.
World 3-1: Warp to World 5
On World 3-1, select any character and fall down the waterfall. There is a door at the bottom. Go inside and find the potion. Throw it near the vase and go inside. Enter the vase, which will warp you to World 5.
World 3-1: Hidden area
There is a location in the water in World 3-1 where you can go beneath a land mass to access a hidden area, by jumping off of a giant spring arrow. If you curve to the side and go above the normal hidden entrance, you should enter an area where you will be falling towards nothing. Keep going right (stay in the air as long as possible) until you reach the edge. You will be teleported to World 1-1 (and gain credit toward World 3-1) where you can gain more red coins and hearts than the maximum. It will only go to the top, but it will be 10 times easier to perfect the level.
World 1-9: Easy lives
Grab a Melon Bug (the bug that curls when you approach) and take him to the Shy-Guy Pipe (where the Shy Guys appear from). Look up and shoot the bug. If done correctly, the bug should fall in the tiny space on the right side of the pipe, between it and landscape. Stand on the elevated surface and make sure you have no eggs. The Shy Guys will pop out towards you, but hit the bug. You will keep getting extra lives until you have 100. Then, get a perfect completion on World 5 and you will get the roulette game. If you get the X3; you will get 300 lives.
World 1-7: Hidden area
Immediately before completing the level, there is a bridge that bends. Get the two Red Coins, then go to the other bridge. After that go on the piece of land with a log sticking out of the ground. Stand on the edge of the log, then shoot an egg straight up. A spring ball should fall. Jump on it and you will go to a hidden stage through a pipe.
World 1-2: Easy lives
Pick up the shell at the start of the level and throw it at the row of Koopas. Quit level and repeat for endless lives.
Level 1-7: Extra lives
Pick up a Rollie-Pollie Guy with your tounge. Do not turn him into an egg or spit him out for anyone until you get to the pipe that spits out Shy-Guys. Once there, spit the Rollie-Pollie Guy out into a 1 (square) hole on the right of the pipe. Once placed, jump onto the platform above and to the right of it. Let the Shy-Guys jump out of the pipe and onto the Rollie-Pollie Guy. Points will accumulate and will eventually give you 1-Ups continually. After a few hours, you will have 999 lives.
Special Yoshi eggs
To get special Yoshi eggs with out having to find special boxes, fire a Yoshi egg in an area that will cause the egg to bounce off the walls and back to you. When the egg returns to you, quickly use Yoshis tongue at the egg. If successful, you should have a special Yoshi egg.
Get your total points for a world to equal to exactly 777, to get 7 extra lives.
After completing the game, an extra level for each world will appear.
Hold Select and press L(2), B, A, R at the level selection screen. A list of bonus games will appear. If you win the selected game you will get a prize.
Alternate ending sequence
Successfully complete the game in hard mode.
Get 1,000 points in a world (100 points on all ten levels including Extra and Secret levels). A star will appear on the game selection screen. Get five stars on that screen to unlock hard mode.
Higher flutter jump
First jump on an enemy and you will be in the air, while you are in the air hold down A and you will get an extra boost.