Note that two games in the Itadaki Street series are often considered direct crossovers between the two series, but to this wiki they're not, being instead games in their own series, only featuring characters from both series. See Dragon Quest X Itadaki Street and Itadaki Street X Mario for details.
Mario Sports Mix
November 25, 2010
In this sequel to Mario Basketball 3on3, Slime, the most recurring enemy in the Dragon Quest series and considered its mascot, is an unlockable playable character and the sixth crossover character, following five characters from the Final Fantasy series that appeared in both this game and its prequel. It's classified in the Tricky category and it's unlocked by playing 28 matches in one sport, or by clearing a certain Flower Cup mission.
In its Special Shot it summons three other slimes, each one with a different color: pink, yellow, and green, referencing the alternate colored Slimes appearing as enemies in the Dragon Quest series.
Its alternate outfits are an orange recoloring, called "She-Slime", and a metallic recoloring, called "Metal Slime", both of which are based on alternate Slime enemies from the Dragon Quest series and are the only outfits in the game that also change the character's name. She-Slime is unlocked by playing 20 matches as Slime, while Metal Slime is unlocked by playing 40 matches as Slime. Like all other alternate outfits in the game they can also be unlocked by beating their specific mission at the Star Cup.
While published by Nintendo, Mario Sports Mix was developed by Square Enix, so they could freely include a character from their own series.