The black Dr. Mario represents Seteth, an instructor who wears a black uniform.
The green Villager minion represents Flayn, the younger sister of Seteth who wears a skirt.
The stage is based on the Garreg Mach Monastery's cathedral, where Seteth and Flayn serve under Rhea's command in Fire Emblem: Three Houses.
The music track is based on the theme song that plays during the fifteenth Crimson Flower chapter of Three Houses where Seteth attempts to reclaim Garreg Mach.
Dr. Mario's increased stats and the battle conditions reference Seteth's overprotectiveness of Flayn after she was injured during the War of Heroes.
Other trivia:
This spirit's Support and Neutral types reference Seteth's role as a party member or an enemy in Three Houses.
This spirit's Air Attack ↑ ability references Seteth's Wyvern Rider class, which allows him to fly over the battlefield and attack.
