These stars are not found in the main courses but are dotted around either the castle itself or mini-levels.
How To Obtain
Secret Slide 1
Once you have obtained several stars, you can unlock the door in the top right of the castle. In here there are three stained glass pictures of Princess Toadstool. Jump into the right side window to enter the secret slide. To grab the star, all you need to do is get to the bottom in one piece
Secret Slide 2
Re-enter the secret slide. This time you have to get to the bottom in 20 seconds or less. If you're struggling then consider these tips:is: Ride down the start of the track and as the wall to your left starts to dissapear, veer to the left and jump off. Control your landing onto a later part of the course and press Z as you are about to land so you don't fall off. This should cut some time off.
In the room with the Jolly Roger Bay painting there are two holes up in the walls either side of the room. Once leads to this mini-level. Collect the red coins for the star.
Wing Cap Switch Course
Collect the red coins in the Wing Cap Switch course.
Metal Cap Switch Course
Collect the red coins in the Metal Cap Switch course.
Vanish Cap Switch Course
Collect the red coins in the Vanish Cap Switch Course
Bowser in the Dark World
Collect all the red coins in the Bowser in the Dark World stage.
Bowser in the Fire Sea
Collect all the red coins in the Bowser in the Fire Sea stage.
Bowser in the Sky
Collect all the red coins in the Bowser in the Sky stage.
Basement Rabbit 1
Collect 20 stars to make a rabbit appear in the basement tunnels. Catch it for a star.
Basement Rabbit 2
Collect 50 stars to make the rabbit reappear in the basement tunnels. Catch it for another star.
Speak to the Toad next to the entrance to Hazy Maze Cave
In the ring corridor past the last locked door, across from the door that leads to the entrance to Tiny-Huge Island.
Through the star door that requires 50 stars at the side of the huge clock.
Over The Rainbow
In the room through the 50 star door where the large clock is there are two alcoves up in the walls to the left and right. Once leads to this stage, where 8 red coins gains you a star.