Thwomper Room, one of the free-for-all minigames in Mario Party 9
Like previous Mario Party titles, two to four players move around a virtual board and play minigames. A new gameplay element in all of the boards is that all four players move around together in one vehicle. The number of spaces the player moves is determined by a roll of the dice block found within the game. Instead of trying to collect coins to buy stars, players receive Mini Stars if they pass by them. Whoever collects the most Mini Stars wins the game. While doing that, players must also try to avoid Mini Ztars, which deduct their current amount of Mini Stars. Mini Stars and Mini Ztars are replaced with bananas and Z-bananas on the board "DK's Jungle Ruins."
Minigames have a larger focus on the gameplay than they did in the previous game. However, the minigames don't appear after everyone moves, but only when a player ends up on any of the spaces or events that triggers a minigame. A person can play on solo mode to unlock the final stage, as well as two playable characters.
Another new feature is that each board culminates in a boss battle that is played with all players in the vehicle. There is also a boss battle at the halfway point of a board. There are 82 minigames in Mario Party 9, divided into five categories: Free-for-all, 1-vs.-Rivals, Bowser Jr., Boss Battle, and Extra.
At the end of each stage, the number of Mini Stars the player collects is converted into Party Points, which can be used to buy new stages, constellations, vehicles, difficulties, and sounds in the museum.
Mario Party 9 features twelve playable characters, with two (Shy Guy and Magikoopa) being unlockable through the Solo Mode.