you need all the stars,in this case a 150 stars then you go outside the castle the cannon will open and you can shoot yourself onto the castle roof were a wing cap,3 1ups,and yoshi.
it is not stars it is a world
By getting a cannon or by winning the fifth castle and then the sixth castle.
All you have to do is go to the world 2 castle and beat the boss with mini Mario
Wot To Unlock Castle Collet 40 Star Coins And Not Shine Sprites
you have to complete the last castle but you have to do it all in one to go back and unlock them.
Im not sure but I think you have to get all 150 power stars.
You must collect all 150 stars, then it will automatically open.
You play the game.
To unlock them you after collecting 12 stars look up in the castle circle and activate the red switch to unlock all ? blocks.
You cannot unlock Yoshi in Super Mario Galaxy; he is not in the game. Yoshi will, however, be unlockable in the upcoming sequel, Super Mario Galaxy 2.
Birdo is not unlockable in Super Mario Galaxy.
You go to the top of the castle and defeat Bowser. After you have defeated Bowser you will have completed the game. If you did that and you won. CONGRATULATIONS