Yoshi's rabbits
The character Yoshi has seven rabbits to collect. Most of them are outside the castle. First go to the bridge directly outside the castle. On the left and right side you'll find the first two rabbits, and at the far end of the bridge will be the third. Head to the tall flowers on the right of the castle. Hidden here is the fourth rabbit. Go the bottom of the drained moat for rabbit No. 5, then head to the hedge maze for No. 6. Unlike the rest, the final "glowing" rabbit is inside the castle -- just head to the hallway that leads to "Lethal Lava Land."
Rabbits for Mario
Two of Mario's seven rabbits are outside of the castle -- one located on the left of the bridge, and the other at the bottom of the moat. In the hall that leads to "Lethal Lava Land," you'll find two rabbits, while the "Jolly Roger Bay" room has one. Take the main staircase to the second floor to find the next rabbit. And while you're up here, head to the large mirror room to collect the last glowing rabbit.
Finding rabbits with Wario
Wario's first rabbit is outside, on the far right side of the castle -- simply walk along the side of wall until you find it. Inside the castle, head to the "Whomp's Fortress" room and collect the second rabbit, then head to the basement and look near Toad for the third. Next go the castle's ghost-filled courtyard for Wario's fourth rabbit, and then back inside to the second floor. From here, access the room to "Tiny Huge Island" and collect the next rabbit. On the third floor of the castle, you'll find a rabbit next to "Tick Tock Clock," as well as the final glowing rabbit in an alcove across from the "Rainbow Ride."
Luigi's Rabbits
Luigi's rabbits are slightly more difficult to discover, especially the last glowing rabbit, which you'll need 150 stars to access. Once all 150 have been collected, a cannon will appear outside the castle that you can use to shoot to the top of the roof. This is where you'll discover the game's final rabbit. But first, collect Luigi's rabbits from the entrance of the hedge maze, the room to the "Bob-omb Battlefield" and the bottom of the moat. To find the rabbit In the courtyard, you'll need to double jump from the brown ledge. Rabbits No. 5 and 6 are behind the wooden door on the second floor, and in the room with the giant portrait of Mario.