not sure if this counts since miis are in the game, but strangely they dont have their own classic mode, so ill give my idea of one of em. Mii Brawler: Fashion show (battles will contain characters capable of wearing many costumes.)
stage 1: vs. Pokemon trainer male and female, colours 7 and 8 (these represent X and Sun, which had costume changes.)
stage 2: vs. male and female Villager
stage 3: vs. 3 Links, with his various outfits.
stage 4: vs. 4 Inklings (with 2 mii gunners as allies using the splatoon costumes)
stage 5: vs. 2 shulks, with one of em being in his trousers
stage 6: fighting miis horde battles. (10-12 will spawn, each wearing a completely different costume)
boss: Master hand & Crazy hand.
I hope this looks alright, it was tough to choose between shulk and mario for stage 5. tho its possible all 3 miis could use the same kind of classic mode, mabey with different costumes used for stage 6.