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.
If you beat every mission, it will give you all the stars, of course. Remember, after you get all 120 stars as Mario, you unlock Luigi. After getting all 120 stars as Luigi, you unlock a bonus star for Mario and Luigi, giving you a grand total of 242 stars to shoot for!
get all of the stars
I've got to stars and this is how: unlock all worlds, get all the stars (in every world), unlock all the shortcuts and extras such as mushroom huts.
Get all 150 stars
Collect all 120 stars.
get all the stars to unlock the cannon
Well I Dont Really Know But I Know That You Need All The Stars To Unlock Waluigi!
figue it out
Yes, Luigi is playable in Super Mario Galaxy. You unlock him after getting all 120 stars as Mario.
Get one or more stars in all 150cc WII cups
Of course not! My friend got all 150 stars but not him.
There are two. Mario and Luigi. You need to unlock Luigi by collecting all the stars and beating bowser again.