catch all the golden bunnys then you'll get the key, its a star :D
You have to unlock Luigi and then use his invisibility power to go through the mirror, if thats what you are asking.
no but you CAN beat the first bowser battle and he will give you a key and not the basement is unlocked!
Go in the bushes, then you'll see a rabbit with a key. Just use your tongue and grab him, and he will give it to you.
To catch a rabbit, attack it (A) at the right second to nab it. If you are successful, it will give you a key to unlock a new mini-game.
If you mean that door in the rec room in Super Mario 64 DS with the number 8 on it, you just need to get 8 stars and then it will open. The course with Goomboss, who holds the key to the room where Mario is locked, is behind this door.
Beet bowza
yes
open a door with a lock in the area you obtaned the key in
dounnut plains 1
fight the 2nd bowser
You do a favor for Merlee
To Unlock Mario, you need to get 8 stars and head upstairs to Princess Peach's room, and go in the door with the 8 on it. Now you will see a window and a painting with Mario in it, jump thought that and explore around. After you find the Gomboss on a tree stump, he will chase you in a circle, ran around the stump, until you get to the back of Gomboss and swallow one of the Gombas. Run back around and hit the Gomboss with the egg. You need to repeat 2 more times!! After he will give you a key to unlock Mario!