Superstar Showdown is the final minigame being played at the end of the Story Mode, or Star Battle Arena found in Mario Party 8. Bowser is good to his word and gives the player back the Star Rod. At the last second, Bowser has second thoughts and challenges the player to the final match. The player is pitted against him in space. If the player is defeated at any time, the player can try again. If the player starts again, Bowser keeps the damage the player has dealt to him.
This minigame is unlocked only when the Star Battle Arena is completed, and then it is playable in Minigame Mode.
This is a one-player game. Bowser has 10 Heart Points, and the player has 5. While Bowser blasts fireballs, the player must hold the Wii Remote up, and swing it around to charge up the Star Rod, while dodging Bowser's flames. After it is charged, the player will swing down his or her arm to throw the energy ball. After hitting Bowser three times, the game goes to Phase 2.
Now Bowser has two Bullet Bill launchers. They fire around 6 Bullet Bills each time. This makes it harder for the player, as he or she has to dodge the missiles. After hitting him three times again, the battle enters Phase 3.
This is the last phase. Now, in addition to the weapons he had before, the Koopa Clown Car will have a laser blaster, which will rotate, sending beams out. The only way to dodge these is to get in between two of them. Also, the Bullet Bills will become red and move faster. When Bowser has two lives left, he will fire a large fireball, in addition to the other attacks. After blasting Bowser one more time, the player beats the game.
After being hit by the final blast from the Star Rod, Bowser, still inside the Koopa Clown Car, is sucked downward into a Black Hole-like vortex.