When you get the 100th coin, a power star will appear whenever you are onto of your head.
The 100 power star missions suck because the coins are too far apart from each other, most of the maps are too large, and the coins are very damn scarce. Each picture has six stars (one hidden star which is the 100 coin stars). Speaking of those, you get power stars throughout the Castle by jumping into pictures and finding the power star in order to get further in the Castle to save Princess Peach for the one millionth time. Sometimes the camera will be blocked by the map or it will be in the other direction which blocks the platforms you need to see in order to get a power star. I know this game came out during the beginning of the 3D age of gaming, but the camera control is horrible (Unfortunately, games today are almost always 3D). The other problem I have with the game is the camera control. The other caps like the metal cap and the invisible cap aren't very helpful and you hardly get to use them. I hate it because the control is awful and it's really f*cking hard to get red coins. The only power up I hate is the wing cap.
Such as the power ups which aren't very useful and you only use them a few times. The game itself is a great time with some flaws. Super Mario 64's soundtrack is great! My favorites are Bob Omb Battefield, Dire Dire Docks, Slider, Cool Cool Mountain, Bowsers Road, and the ending theme.