There are seven glowing rabbits that randomly replace each of the character's mini-game rabbits. After catching all seven, you will receive a key that unlocks the white door to the right of Wario's. You will receive a Star. In order to find the glowing rabbits, you must first find all the regular rabbits for each character. The location of the glowing rabbits is as follows:
Rabbit 1 Catch it with Luigi. It is found in the underground hallway near the Lethal Lava Land course.
Rabbit 2 Catch it with Yoshi. It is found in the garden on the outside of the castle near the bushes.
Rabbit 3 Catch it with Wario. It is found in the hall of the Tiny-Huge Island course.
Rabbit 4 Catch it with Mario. It is found on the staircase leading up to the Tick-Tock Clock course and the Rainbow Ride course.
Rabbit 5 Catch it with Luigi. Found in the Bob-Omb Battlefield hall.
Rabbit 6 Catch it with Wario. Found in the same place you found it with Wario. It is found in the hall of the Tiny-Huge Island Course.
Rabbit 7 Catch it with Mario. Found in the Jolly Roger Bay hall.
To unlock to glowing rabbits, you must find all seven rabbits for each character. Luigi only has six, as his seventh one is on the roof of the castle which cannot be accessed until all 150 Power Stars are recovered. After this, eight white rabbits will appear at random. For the most part, each character has about two rabbits. Generally, the glowing rabbit for each character can be found by going to all the rabbits, then the last one is the glowing rabbit. Once a rabbit is found that is glowing, you do not have to go to that one to make the last one glowing. There is no order on the characters; just start with Luigi and go to all rabbits until a glowing rabbit or all have been checked. Then, switch to Mario, Yoshi, and Wario. Continue until the final rabbit is found. The eighth glowing rabbit will give you a key that will open the door next to Wario's refereed to as "The Empty Room." This room contains a Power Star and nothing else.