Secret
Got to the room on the first floor with the entrance to the level with the sunken ship picture. There all small square holes on the walls. Jump in the one on the left to get a 1-Up. Jump into the one on the right to enter the Castle Secret. To earn a Star you must swim through the tank and get all eight red coins. To get air, you must grab the other coins -- their is no way to get out of the water.

Unlockable: Luigi
After unlocking the red ! boxes, go to the castle courtyard. Punch the giant boo with the cage inside of him to enter Big Boo's Haunt. Obtain the first star by defeating all the Boos to get the staircase. In the second goal, as Mario, go up the stars and into the room with the single bookshelf. Use the fire flower to float up to the room above, where you'll find a Luigi painting. Jump through the painting and defeat Big Boo to get Luigi's key.

Unlockable: Mario
Once you obtain 8 stars, enter the rec room and unlock the 8 star door. Jump into the Mario picture and defeat Goomboss to obtain the key for Mario's Room.

Unlockable: Red [!] Boxes
After obtaining 14 stars, stand on the Sun carpet in the main plaza. Enter first person view mood and look up to the beam of light. In the new world, stomp on the red switch in the middle tower to unlock the red [!] boxes.

Unlockable: Wario
After obtaining 30 stars and defeating Bowser for a 2nd time, head up to the second castle floor and enter the room where Snowman's land. On the left you'll see a Luigi painting, but its reflection in the mirror will be a Wario painting. Get the flower to turn invisible and walk through the mirror to appear on the opposite side. Jump into the Wario painting to enter the level. Defeat Chief Chilly to obtain the key for Wario's Room.

Castle: Secret Star
Stand on the sun platform in the middle of the main room in the castle as Mario. Gaze up at the sun above the final Boss door. You must perform this trick with Mario because he is the only person that can fly. Inside, you must collect eight red coins and a Star will appear on the center platform. Note: You can only receive this star after you reach a certain point in the game. You will know you have reached this point when the sun shines through onto the plat.

Mirror Room: Secret Star
Once you have access to the second floor, visit the Mirror Room with Luigi. Grab a flower and walk into the mirror to pass through it. Go straight to the door in the background and it will open, bringing you to a completely white room with a star in it. To get back into the main area, grab another flower or go to the right to free Wario (if you already have not done so).

-- Mini-game requirements --

Yoshi
Hide And Boo Seek: One rabbit
Puzzle Panel: Two rabbits
Boom Box: Three rabbits
Tox Box Shuffle: Four rabbits
Which Wiggler?: Five rabbits

Mario
Sort Or 'Splode: One rabbit
Trampoline Time: Two rabbits
Shuffle Shell: Three rabbits
Bounce And Trounce: Four rabbits
Connect The Characters: Five rabbits
Shell Smash: Six rabbits
Trampoline Terror: Seven rabbits

Wario
Coincentration: One rabbit
Bingo Ball: Two rabbits
Psyche Out!: Three rabbits
Slots Shot: Four rabbits
Lakitu Launch: Five rabbits
Intense Coincentration: Six rabbits
Giant Snowball Slalom: Seven rabbits

Star bonus
Obtain all 150 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 onto the roof, where you will meet Princess Peach and get 100 lives.

Stop the clock level
To stop the clock level on the third floor of the castle, jump in at exactly 12 o'clock. Go in at 3, 6, or 9 o'clock to make it slow, medium, or fast; respectively.

Classic Mario Game Reference
When the game starts, go to the rec room. You will hear the level selection screen music from Super Mario Bros. 3.

Secret Star
Go to the the rec-room (in the castle up the stairs the door to your right).Go up to toad (don't talk to him)then turn to your left there should be a painting of an island, jump into it you will have to collect the blue stars and then a star will appear in the glass sphere.

Unlock Wario Mini-Games
To unlock these mini-games, catch rabbits at the following locations as Wario:

Giant Snowball Slalom-In the alcove opposite Rainbow Ride.
Bingo Ball-On the right side of the castle when facing it. (Near the trees)
Coincentration-Near the entrance to Whomp's Fortress.
Intense Coincentration-Near the entrance to Tick-Tock Clock.
Lakitu Launch-Near the entrances to Tiny-Huge Island.
Psyche Out-In a corridor near Lethal Lava Land.
Slots Shot-In the courtyard behind the fountain.

Unlock Luigi Mini-Games
To unlock Luigi's Mini-Games, catch rabbits at the following locations with Luigi:

Memory Master-Near the entrance to Wet Dry World.
Lucky Stars-Near the entrance to Bob-omb Battlefield.
Mario Slot-In the secret room with the Mario painting.
Mushroom Roulette-In the area with the columns used to drain the moat.
Pair-a-Gone And On-Outside in the hedge maze. Picture Poker-In the courtyard above the entrance.
Super Mario Slot-On top of the Castle. (You need 150 stars)

Two stars from Toad
If you happen to miss out on the star that you get from defeating the Boo's in the courtyard and getting their red coins, dont fret. You can still get 150 stars. It is simple, go to any one of the three Toads that gave you the other stars (the one in Hazy maze Cave level entrance, near Tick tock the Clock entrance, and near tall tall mountain entrance) and talk to them, one of them will give you the star that you had missed out on earlier. This does not work for stars that you don't want to get like secret level stars on regular level stars, it only works for the Boo's courtyard star because it was a star that dissapeared near the beginning.

Easy Coins
In any level where there is a small wooden post sticking out of the ground, pound it three times to have 5 coins revealed. This can be very helpful when trying to get extra lives or a 100-coin star.

Don't Decrease Card Game Record
When the hands are revealed in any of the card games that has a record that increases when you win and decreases when you lose, look at the opponent's hand before it displays who wins or loses and pause. If you lost the hand hit quit and reenter the game. You'll have lost however many coins you bet but your record will remain intact.

Make Yoshi Grow Big
Normally in a level, a moustached player can brake a box and there will be a mushroom inside. Try this with Yoshi however, and he'll not be able to break it, therefore not getting the mushroom and not growing big. Solution!

1. Start level as yoshi
2. Get a cap
3. Make sure an enemy is close to the mushroom box
4. Break the box
5. Get ingured by the enemy
6. You'll lose your hat and return to Yoshi, now grab the mushroom before it's gone!

Sea Monkey
To use this cheat, you must be Wario, or at least another playable character wearing a Wario cap. First have the owl lift you to the top of the mountain in Tall, Tall, Mountain, then hit the red box. Grab the Power Flower, and you will turn metal. Go down the waterfall, and you should be where the monkey is. Grab him, and go in the water. Once you're normal, you'll float in the water. Get out, and what the monkey will say, "Ukkiki...wakkiki...kee kee! Ha! I snagged it! It's mine! Heeheeheeee!" If you're not playing as Wario, you'll turn back into Mario, Luigi, or Yoshi. But the weird thing is, the monkey will be wearing Wario's cap underwater!

-- Tips and Tricks --

The Great Flying Mario* Trick (very hard to do) FIRST you must find a Goomba near a cliff. Then long jump toward the Goomba, and the cliff. If done correctly, Mario* shall long jump toward the Goomba, and off the cliff!
* Means Mario, Luigi, Yoshi, Wario

Silver Rabbits Galore
Most people have been waiting for a quicker way to get the 8 Silver Rabbits, well here you go! Play as Yoshi and go outside the Castle, where the three rabbits are. If one of them is shiny (or even two or three), catch'em and go in the front doors and then go out again. Repeat this process until you get the key. Then go to the room with the character changing doors and insert the key in the White Door to claim your prize!

Never Ending Jump
While battling Wiggler on Tall Tall Mountain, jump on his back and don't move the D-Pad and you'll keep on bouncing!