Bowser: nothing super serious or complex, Bowser jr got Lost and you must find him, maybe a bigger threat that’s menacing the Mushroom Kingdom have him and you may even ally with the gang (Mario, Peach, maybe other characters like Luigi, Daisy, or other original or returning characters) but Bowser doesnt care about saving the Mushroom Kingdom, only wants his son back and the rest can care about the Mushroom Kingdom
Yeah i know, how original but i Will ever think that Bowser is a great character to explore in a non villanous way
Orangutan from Sekiro. From the perspective of his younger life would be really interesting I think. He’s a focal point for the other existing characters and fighting a final battle your are destined to lose could be an interesting experience. Plus you could add Shura powers instead of the prosthetic.