To describe Bowser in one post would be impossible so this will be so much less than it could be. The staggering amount of information on Mario’s greatest enemy is… staggering? In SMB3 we’ve seen his kids do all of his dirty work but eventually you’re facing off against King Koopa in his own home on his own terms. You’ve got to avoid all of his fireballs and trick him into smashing the ground beneath you so he falls to his (apparent) doom.
A neat trick to make this easier to to disable his fireballs. That trick isn’t easy but it’s worth it. The other big trick is that Bowser’s feet don’t damage you. If you’re small Mario or do a duck slide you can go right through him without being hit. If you use both of these tricks to your advantage then beating Bowser is a breeze.