You didn't really specify what type of game this would be. Did you have a platformer in mind? Would it be 2D or 3D?
I like this idea. Bowser is world-renowned and yet he's never really had his own game. Platformers tend to have agile characters that can move quickly, so Bowser doesn't seem like the best fit for that type of game, but maybe a beat 'em up of some sort.