From the Super Mario Wiki
The Bullet Bill Capsule is an item that first appears in Mario Party 5, where it can be thrown to a space on the board or used on the player for five coins. It allows players to ride Bullet Bill the number of spaces as determined by the Dice Block, taking thirty coins from everyone in its path, making it the replacement for the Bowser Suit. In Mario Party 6, it is known as the Bullet Bill Orb. Players can use it only on themselves, free of charge (it costs twenty coins at the Orb Shop). Again, the effect is still the same, except players steal only twenty coins from opponents.