Eight glowing rabbits will randomly replace each of the character's mini-game rabbits. Once you catch all eight, you will earn a key that unlocks the white door to the right of Wario's, leading to a Star.
In order to make the glowing rabbits appear , you must find all the regular rabbits for each character. The glowing rabbits can be caught in any order.
The quickest way to catch all eight glowing rabbits is by using Yoshi and going outside (not the Boo courtyard). Yoshi has five rabbits outside. Catch all the glowing rabbits, then re-enter the castle and exit again. Repeat this until you catch all eight glowing rabbits.