When your in Tall, Tall Mountain, go in as Mario, go to the top, get the wings, fly down to the botom and to that gap where the cannon is. Walk to it, walk back, and go to the spot at the emd, which is square-like, you'll be teleported to another space, AND YOU WILL BE UNDERWATER. I'm not lying, you will be underwater.
Though if you swim up, the glitch will end and you'll be falling. I'm telling you this is an awesome glitch

On the mission "blast to the stone pillar" on jolly roger bay, enter the painting as mario. Then, go left, and get the power flower. Use it, keep tapping B, and float to the star.

Note: this only works if you have turned on the ? Blocks.

When you experence (find) a light in the main hall press X and look up bye

When Luigi deals you a hand, and you don't like it, before you place a bet, quit the Mini-game. You will not lose or win any coins, and you can play again for a better hand. With this, it's easy to get a higher score safely.

To unlock wario you must go into the mirror room as luigi. Get one of the power flowers and go through the mirror. Then simply jump into the wario painting and defeat the boss.

To unlock luigi you need to go to Big Boo's Haunt as mario. Go upstairs and go into the room on the far right. Get the power box and float up to the platform. Go through the door and jump into the luigi painting and defeat the boss.

About the submitted cheat about my 30 secret star list, there were some that were incorrect because I didn't check on the DS. So these are the corrections on some of them
13 & 29. Where you save Mario, Collect the red coins and right of where you start the area, where the switch star is, step on the switch and wall jump where the star is on the map. 25, 26 & 27 (Toad's stars)
25. Near the Entrance to Hazy Maze Cave, as Yoshi.
26. On the second floor, under the stairs to the top tower, as anyone.
27. Near Tick Tock Clock, in the top tower, as anyone

Mario Cheater

When you are playing, press start and close your ds. Then, listen to what mario says.

To kill browser let him charge up to you, and wait till he is wobbling, kick him NOT PUNCH and the second way, let him charge at, you but run round in circles, wait till he is tired, then grab his tail, and fling him out of the arena on to the spikes that hurt him more or out into the darkness! (note you have to do it two times)

If you go into the main hall you will see a mat stand on the mat with mario and go into first persons view (press z). The look up to the light you will need more than eight stars to do this but when you look into the light you will be in another level. Go to the middle castle in this level and activate the ? Switch, then go over every level and there will be extra boxes.

First grab the wario hat and grab your opponent with the A button after you knock them down by punching then, after you grab them take tham to the edge of Battle fort were the red brick wall is keep on throwing them and kicking them on the wall.

There is, believe it or not, a cannon outside of the castle that you can unlock after collecting all 150 stars. The cannon is located by the lake by the steep sandy hill off to the left when you're facing away from the castle. The cannon can be used to blast yourself to the Castle roof, where you can find one of Luigi's minigame bunnies.

Play as luigi:

get the power flower in the mirror room
go through the mirror
go trough the door
hey presto the white room is all yours
NOTE:there is a star in there

Unlock Mario Key:
Defeat Goomboss behind 8-Star Door in the Rec-Room

Unlock Luigi Key:
Defeat King Boo in Luigi's Painting on the 3rd Floor of Big Boo's Haunt

Unlock Wario Key:
With Luigi in Mirror Room, hop into Wario's Painting and Defeat the Giant Ice Bully

Unlock White Room Key:
Catch all the Shinning Rabbits

Unlock Cannon:
To access the cannon outside the castle, get 150 stars. There are three 1-ups, a cap and Luigi's rabbit.