To get Mario:
You have Yoshi and you go were all the doors with letters on them L (Luigi), M(Mario) & W (Wario). Then there is a door without it just in front of you. Go to the game room, to get Mario you have to have 8 stars. Go to the room with the #8 on it and there will be a Mario pic, go into the pic and beat the level and you have Mario.
To get Luigi:
Go to the courtyard and you'll see a Boo (ghost). Go into the door that the boo went in and you'll either see a big Boo or just see smaller ones. If you see smaller ones you get the red coins. You and a star will appear and then you get the star. Go out the door then go through the doors again and you'll see a big Boo on either side. Kill the big one and go into the cage. Its a level so you do the first level then there are stairs. Go up the stairs after getting the star, go to the right then go to the other right door after turning right. Get the ! box and get to the top (you have to have Mario) and press R to land. You'll see a Luigi pic, go into it to beat the level and get Luigi!
To get Wario:
Go to the top floor with Luigi and go to the mirror room. Then eat the flower. Go to the Wario picture where the guy is wearing yellow, go into the pic!
Tracing a character:
In the main menu touch the character then touch the hand that is pointing. You will have free drawing acess. To trace the player press L or R.
(supplied by: daniel cataldo)
There are two stars on the secret slide. One is at the bottom of the slide. When you start the slide, go down it using the sliding kick move. (you crouch while running then push attack before you go down). When you past the line a star should appear, take it and you got a secret star.
(supplied by: jmenolan)
Refill Power Bar Easy:
Just jump in the water,go under and come up it will fill all the way up.
(supplied by: Luigi Master)
Get lives easy:
Start by switching to Wario. If you did not unlock him yet you can't get these lives. Anyway once your Wario go into course 12 Tall Tall Mountain. Pick Mission 5 or over. Now start going up the Mountain. Go past the red coin mushrooms and soon two black boxes.Break them open with Wario. One of them contains a mushroom (not a 1 up mushroom) The rest is simple when Large run over the moles.
(supplied by: chris)
After obtaining 30 stars, enter through the door into the mirror room. Go to the side that doesn't have the portrait of luigi. The wall looks solid but its not...try jumping into the wall.
(supplied by: ye rite)