Easy Stars!
You might already know this, but if you go in one world and collect 100 coins, a secret Power Star will appear! Nab the star, and then just complete the level and you will leave with two stars for the price of one! Or if you die, you will still have the 100 coin star, and then go back in for the other one!
We have more cheats and tips for this game here, Super Mario 64 DS cheats
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