Mario Series:
Mario as Cuphead
Luigi as Mugman
Peach as her New Nintendo 3DS appearance
Bowser as Dry Bowser (or just Dry Bowser)
Donkey Kong as his New Nintendo 3DS appearance
Wario as his WarioWare: D.I.Y. appearance
MLP Equestria Girls Series:
Rainbow Dash as Mario
Fluttershy as Luigi
Rarity as Wario
Twilight as Yoshi
Applejack as Rumor Honeybottoms
Pinkie Pie as Baroness Von Bon Bon
Sunset Shimmer as Ms. Chalice
Juniper Montage as Mr. King Dice
Adagio Dazzle as The Devil
Cuphead Series:
Cuphead as Mario
Mugman as Luigi
Baroness Von Bon Bon as Princess Peach
Cala Maria as Princess Daisy
Hilda Berg as Rosalina
Djimmi the Great as Toad
Rumor Honeybottoms as Honey Queen
And of course, Mariclaw(me) as Cuphead
Update: I added the crowns of Bon Bon, Cala Maria, and Hilda to look like the three princesses. I also included the cape of Honey Queen to Rumor. Now it looks perfect, everyone is enjoying Halloween!
Happy Halloween!!!
Mario characters: Nintendo
MLP characters: Hasbro
Cuphead characters: Studio MDHR
Rainbow Dash, Fluttershy, Rarity, and Twilight in Mario costumes: myself
Applejack, Pinkie Pie, Sunset, Juniper, and Adagio in Cuphead costumes: 15432
Cuphead and Mugman in Mario Bros. Costumes: Twin-Gamer