Bobinator
My thoughts on your posting
Here's mine: Robotnik's/Eggman's Revenge. One player controls Robotnik in one of his contraptions, and a small number of players take the role of the player characters. Robotnik has to use his attacks to kill all the players before he takes 8 hits. You could either use the bosses from the SP mode, or make up some new ones specifically for this mode. The challenge would be you being this slow target who NEVER gets more than 8 hits, with a big variety of attacks, going against small, fast targets who are sitting ducks without rings.