Mario Kart, which took items and characters from the Mario world and made it possible.
Why not Mario FPS?
Throwing a shell down the hall and bounce it pass the door and hit your enemies that way would be pretty funny.
There's bombs of all sizes.
Get a star and run down your enemies like you're in an armored truck, at the same time, you have to watch for it to wear off, like pacman having a large pill.
Spring items that gets you to higher ground.
Pipes for travel. Camping pipes would be funny. Until your enemy popped out of the pipe with a star on.
Different suit from mario world to give unique abilities. Such as racoon suit allows you to turn into stone making you immume to most shots. At the same time, you cannot take any action while in stone mode. So, you could either wait for the enemy to run out of bullets or leave you alone. Or quickly come out of it and retaliate.
The game wouldn't be M rated for lack of gore.
It'll sell millions!
