Although there are 150 stars in total, you only need 70 to beat the final Bowser level, as this is the number of stars you need to unlock this level.
BUT IF YOU LEARN THE SPECIAL CHEAT YOU CAN USE ONLY 50 STARS AND DO WITH ANY CHARECTER :)
Collect all 120 stars and go to the cannon outside. If you are playing super Mario 64 ds get all 150 stars and go to the cannon outside.
it is not stars it is a world
Get all 150 stars
All 120.
You gotta get all of the stars, then the cannon outside will open up.
Im not sure but I think you have to get all 150 power stars.
If you mean the outside cannon you have to collect 120 stars. If you're talking about the ones in the courses you have to talk to a bob-bob buddy (pink bob-bob).
Collect all of the stars. 120 for the Nintendo 64 version; 150 for the Nintendo DS remake.
When you get 150 star you go outside with luigi and go to the cannon, then go on top of the castle and get the rabbit
Collect 120 stars
get all of the stars and then jump in the cannon near the lake.
The cannon is opened outside the castle, shoot to the roof there is three 1-ups, luigis rabbit, and a wing cap