You enter the castle, go up the stairs and to the right, into the door with the 1 on it. Then you go through the door with a large red M on it, then whoever you are playing as exits the room as Mario!
Note: There are comments associated with this question. See the
discussion page
to add to the conversation.
First, you will need 8 stars. Once you have obtained the 8 stars, head to Princess Peach's play room and open the door that has a star with an "8" on it. Once in the room, jump into the painting that...
well before you unlock Mario you have to earn 8 stars. After you earn the 8 stars go to princess peach's rec room. inside the room you will see a door with a 8 on it. when you go inside there will be...
Yoshi- Start adventure mode, skip the story and you get him Mario- get 8 stars, go into the top floor, go to the door that has 8 stars on it, and then go and dodge the enemies, and then beat...