One-up butterflies:
Butterflies may appear on courses 2, 12, and 13. Punch the butterflies to turn them into round black bombs that will chase
Mario. The bombs will explode or turn into one-up mushrooms.

Thousand coin unlimited lives (Japanese version):
During the first meeting with Bowser, avoid him and collect all the coins that appear. After a considerable amount of time, you
should be able to collect 1000 coins. At this point, a green "M" will appear next to the number of lives remaining. From this
point on, when a life is lost, the number of lives increases. The reverse is also true - gaining lives will actually lower the number
of lives remaining. The cheat will end if the number of lives reaches zero, such as when Yoshi gives Mario 100 lives after
obtaining 120 stars. The North American version only allows 999 coins to be collected.

Very big penguin:
Obtain all 120 stars and return to Course 4 (Cool, Cool Mountain). Before entering, select the Big Penguin Race. Begin game
play and jump into the chimney of the house at the beginning of the level. The penguin will be even larger than before.

Yoshi:
Obtain all 120 stars and go outside the castle. Climb inside the cannon opening that is now located where the grating was near
the Fish Pond. Aim to land Mario onto the roof, where he will meet Yoshi. He will speak to Mario, award a 100 life bonus
and a triple-jump move, and quickly leave.

Alternate Bowser message:
Obtain all 120 stars and return to the final fight with Bowser to see a different message.

One-up tree:
Go outside the castle, near the waterfall. Climb the third tree away from the waterfall. Do a handstand on top of the tree to get a one-up. Enter the castle's first floor. Then, return outside and climb the same tree. Do another handstand for another one-up.
Repeat the trick as needed.

One-ups in third Bowser battle:
Walk behind the top left pillar to collect a 1-Up if you lose a life during the battle.

Below submitted by Trina Mans
On level 3 you can make the moma penguin mad by taking the baby (the
right baby) to the mother and she will give you a star but befor taking
the star take the baby and run around the edge of the pond.

For a short cut on the third Bowser level go to the first ferris wheel
and get on it and wait for it to get to the top ( hold Z while doing
this and press A ) and do a backwards flip and you should end up on the
other side of the big toy guy.

Carry Mario's hat in his hands:
Go to Snowman's Land (the second snow world) and allow the big snowman to blow Mario's hat off. Enter the warp that is under a tree, and go back and forth through the warps about three to five times. Return to where the hat was blown off and pick it up. Mario will now be holding it in his hands.

Stop the clock level:
To stop the clock level on the third floor of the castle, jump in at exactly 12 o'clock

Change Mario's appearance:
Wait until Mario's head appears on the opening screen. Press A and use the hand that appears to grab and stretch various parts of his face. Press B to make Mario's head smaller. To keep a previously stretched piece in that position, hold R and select another piece to change.

Easy health refill:
When Mario's energy is low, find water, swim underwater, then get some air. Another technique is to keep collecting coins.

Alternate triple jump:
Obtain all 120 stars and use the cannon to see Yoshi. Mario will be able to perform a different triple jump after you talk to Yoshi. Instead of doing a flip while both feet are sticking out straight, Mario will do a real flip crouched together with sparkles. The sparkles will  protect Mario from damage when triple jumping off a high place.

Flying cap:
Get this get nine stars and defeat the first koopa level. A light will appear from the ceiling in the main area in the castle after the koopa level. Look directly at the light to reach the flying cap level. Fly straight down to the platform and land. Step on the red button.

Steel cap:
Go to the caves level in the other part of the castle. First, make a left then super jump to the other side and open the door. Turn right and follow the path. Super jump to where the huge boulders are located. Reach the top of where the boulders are dropping from. Go through the door and step on the elevator. When the elevator stops, follow the path to the underground sea. Find the sea dragon and get on his back. Execute a super butt stomp on his back, then get on his head. Lead him to the part of land that contains the red outlined blocks and jump on them. Then, go through the door and run to the other stream. Try not to fall in the water. Jump from land to land until reaching the green switch. Stomp on the switch to get the steel cap.

Invisibility hat:
Run through the hall that is flooded and has an unmarked door. Enter the door and find the location where there are two pillars in the water. Super butt slam on both of them. After the water drains, follow the arrows that leads to another room. Go through the door, then find the square hole in the ground. Enter the hole and complete the rest of the level to find the hat.

Mario wearing sunglasses:
At the screen where Mario's face can be altered, press B, then hold R and pull Mario's cheeks up as far as possible and keep them that way. Mario will look like he is wearing sunglasses.

Look through walls:
Walk up to a wall at a certain angle in first person view to see past it.

Shortcut in final Bowser level:
Climb up the "Lego" platform, to reach to a part that levels out just a bit. Get as close as possible to the part that continues to climb, then turn around and perform a long jump in the opposite direction. Mario will land on the checkered platform right before the moving platform with the arrow on it. Using this will allow you to avoid the time and the danger of the flameblowers along the way of the "Lego" path.

Spiral stairs shortcut:
Walk into the castle, walk up the stairs to the door with the key hole, then go inside. You will see a column to the left, just before the staircase starts to spiral. Walk along the wall to your left until reaching the corner where the wall and the column meet. Perform a double jump while still moving in that direction. This should allow Mario to jump through the ceiling and bring him right to the top of the stairs. Although this is not a very large shortcut, it will save a few seconds and some dizziness.

Reaching high ledges:
To reach high ledges, back flip, triple jump, or wall kick.

Extra stars:
Besides the six stars in each course there is an additional a seventh star obtained when 100 coins are collected. There are also stars in the castle. Toad gives Mario a few, as well as the running rabbit in the basement.

Stuck inside of the castle:
After getting 120 stars, use the canon to go on top of the castle. Get the flying cap at that location, then fly back to the canon as quick as possible. Aim for the cloud that is right above the castle's peak. Land on the second ledge of peak. Jump into the wall (facing the castle's entrance) until Mario falls in. Try diving in if you can not get after a few tries, or the whole process may need to be repeated. Once stuck, Mario will be in between the castle's entry way and the first floor. You can go through the doors to change places, but the only way to get out is to get on the main entrance side and walk through the walls on the sides of the doors or jump over the doors.