From the Super Mario Wiki
Holly Koopa is a female Koopa Troopa who appears to be rather wealthy. She is found during the events of Mario Party 8, on the board Shy Guy's Perplex Express. If the player lands on a ? Space that resides on the top of the train, a Shy Guy will appear, announcing that Bandit or Mowz has stolen Holly Koopa's candy. The player must remember which car they last saw Mowz or Bandit riding in. If the player answers correctly, the Shy Guy will award them coins. Another question mark in one of the rooms has Holly Koopa asking the player if she could have a piece of candy. She will pay the character coins in return (if they give her the piece of candy).
Holly Koopa appears in Star Battle number 4. Here, she plays a major part in the battle. The first person who gives her fifty Coins will not only get to be Holly Koopa's number one fan, but also receive a Power Star and win the battle.
The Shy Guy conductor of the train states that he has a large portion of money, and that he is a big fan of Holly Koopa; however, he is too shy to meet her. In Star Battle, when the player meets the Shy Guy conductor, he will give the player ten coins to give to Holly Koopa.