Capsule items replace the old inventory in Mario Party 5, and Hudson throws them onto the GameCube boards. The 2003 party lets a player plant a capsule on a space and change the next roll.
New boards, a set of minigames, and the same star-buying contest keep the party recognizable. A capsule might grow a plant, spring a trap, or move a star, so the board itself becomes the weapon between minigames.
Mario Party 4 had brought the format to the console without this item system. The fifth entry's capsules are the rule change, and the boards are built around them.