Castle Grounds is the first overworld of SM64 Last Impact and what better place to hide some stars than in plain sight. At various points during the game, you will have to complete mini-quests to gain Hidden Stars. Some are more obvious than others, so be sure to check for any new characters that appear out of the blue.
Yoshi replaces toad in the gazebo after Mario has his first star. He traveled all this way looking for some delicious fruits to take home. Where has Mario seen anything that would fill Yoshi's appetite? Perhaps those coconuts by the boat he's been kicking around pointlessly until now? Bring one over, and drop it in the basket. Yoshi will trade you for a pointless star he cannot eat.
The Goomba Bros. have a new plan: to steal Princess Peach. They have been practicing some new strategies that will take Mario down for sure. Or...maybe not. They first make their appearance after Mario has several stars under his belt, in front of the ancient columns. They will try to attack Mario using two new strategies: Triangle and Pokey formations. They even have a special bonus exit strategy, the Pancake!
The Goomba Bros. simply won't give up!. They have taken it upon themselves to guard the castle stars.They will do what Bowser couldn't and defeat Mario! They even brought along some new gadgets to help them! Too bad they were only wonky prototypes. Maybe next time Goomba Bros., maybe next time..