Mario Sports Mix is a Mario sports game for the Wii featuring Mario and company competing in four sports: hockey, basketball, dodgeball, and volleyball, along with the Final Fantasy characters who have appeared in Mario Hoops 3-On-3 as well. Slime, a Dragon Quest mascot, makes an appearance in this game, too. This game is developed by Square Enix, who also developed Mario Hoops 3-on-3.
The game supports the Nintendo Wi-Fi Connection feature, which enables players to play with other players in their region. To save any game data, three blocks of memory have to be used on the Wii system. However, due to the game's Wi-Fi compatibilities, the game data is copy protected, which means it cannot be transferred onto other Wii systems.
One day in the Mushroom Kingdom, Toad is gardening flowers when suddenly, the sky turns dark, and a strange object falls from the sky and crashes. Toad is worried about the situation, so he, along with some other Toads, rushes to the crashed object to examine it. The Toads find four colored crystals: a red crystal with a basketball in it, a green crystal with a volleyball in it, a yellow crystal with a dodgeball in it, and a blue crystal with a coin in it. While observing the mysterious crystals, the Toads suddenly come up with an idea of introducing new sports - Basketball, Volleyball, Dodgeball, and Hockey - to the Mushroom Kingdom. The Toads also organize tournaments for the four sports. The best players of the tournament earn a prize: one of the four crystals that fell from the sky. Mario, his friends, and his foes are ready to play sports and enter the tournaments to find out who are the best players of the Mushroom Kingdom.
When the players' team wins the Mushroom and Flower Cups, and gets to the end of the Star Cup, everything seems to be normal, but in the final round, a Star Ship appears and the players' opponent turns out to be Ninja in disguise. Ninja steals the trophy and jumps onto the Star Ship. The players follow Ninja to get the trophy back. They end up playing against the Final Fantasy team, while the Star Ship flies through space. When the players win against the Final Fantasy team, they receive one of the crystals that fell from the sky. The leader of the team uses it to power the Star Ship and take the team back home.
After players receive all four crystals, the crystals merge and turn into a dark, glowing crystal. The dark crystal takes the players to another area. In this area, players encounter the Behemoth, a creature from the Final Fantasy series. The players must defeat the monster before it defeats them. When the players defeat Behemoth, the dark energy from the dark crystal disappears and turns into a rainbow-colored crystal. The players use the crystal again to power the Star Ship to take them back home.
Sports Mix mode's story is highly identical, except after the players' team defeats the Final Fantasy team, the three Sports Mix trophies that they receive will end up merging into a dark crystal. That crystal also leads them to an alternate dimension, where the Behemoth King is found. Similarly with Behemoth, players have to defeat the Behemoth King before it takes them out. When the Behemoth King is defeated, the crystal's dark energy disappears, and it turns back into a rainbow crystal. The players use that crystal to power the Star Ship to take them back home.