What are the secrets in super Mario galaxy?

you need to get all the red power stars then by beating the level in the gateway dome... you get a power up. The mission is to get the purple coins. The red luma will let you use a power up that looks like a small grand star that's red it allows you to fly! FLY I SAY! Then wants you beat the level... the secret is that power up called red star. If you unlock luigi though... You look like Mr. L! Your allowed to use it in the observeitory!