Bowser is a tough Mario opponent and he has Giga Bowser form, which can cause a lot of damage. That being said, Charizard is simply the more powerful fighter here. He has a decent amount of resistance to fire attacks and Bowser will have a tough time landing any physical attacks due to Charizard’s speed. The Pokemon can afford to stay from afar and throw out his long range attacks for a while. A few hyper beams should do the trick here! Charizard wins.