The Behemoth is a recurring enemy from the Final Fantasy series, and is the final boss in Mario Sports Mix. If the player defeats the Final Fantasy team (composed of Ninja, White Mage, and Black Mage) at all sports, an extra challenge is given to the player, where they must face off against Behemoth.

During the Behemoth battle, the player and his or her teammates must work together to fully deplete Behemoth's health. They're each given a life meter, which will deplete if any of them get hit by Behemoth's attacks. To fight Behemoth, players use their various skills from all the sports, while having access to an energy weapon that's shaped like a Hockey stick, along with the ? Panels. The ? Panels will either contain a meteor (which is used like a Basketball, Volleyball, and Dodgeball), a Coin (used to strengthen the player's attacks), a Green Shell, or a Bob-omb. These items have to be used directly on Behemoth to affect it.

Additionally, when the Special Shot meter bar is full, the player can have their team perform a special move that's unique to this fight to inflict some decently good damage to Behemoth.

Behemoth does feature some various attacks that the player must watch out for. If the player stays too close to Behemoth, they may risk getting attacked by its claws and/or tail. Behemoth may also do a body slam, or charge right into the player. The player can be clued to when Behemoth will start charging when it roars. It can also release fireballs, lightning bolts, and meteors at the player as well. Fortunately, the player can stop most of Behemoth's attacks by damaging it.

If any players have their health fully depleted, they'll be knocked out temporarily, but as long as one player still has some health remaining, they can recover and rejoin the fight again with a small portion of their health recovered. Fortunately, teammates can't lose health from their own attacks.

When the player and their team fully deplete Behemoth's health, it'll get knocked out and vanish, which gives the player an extra mode for winning; Sports Mix mode.

A harder version of Behemoth, known as Behemoth King, can be fought by clearing the Star Cup in Sports Mix mode.