I have three new characters Nintendo could add to Mario kart 8 Deluxe Hammer bro, Birdo, and Diddy Kong they could even have fire bro be an alternate costume for hammer bro :
Adorable Kids DIY Mario Villains Group Costume | Primary.com | Primary.com
Hammer bro Mario | Super mario bros, Super mario, Mario bros
My Life in Transition: A Super Mario Brothers Halloween
Hammer Bro....Super Mario Bros. | Mario and luigi, Hammer bro, Super mario
Otakon 2016 Hammer Bro Cosplay by J-Greene on DeviantArt
Hammer Brother Cosplay | Mario Amino
Hammer Bro | Super Mario Exploration Wiki | Fandom