THE BREAKDOWN
WEAPONARY
Both combatants bring to the table formidable claws, teeth, and nasty breath.
THE EDGE: BOWSER
Bowser plain and simple outclasses charizard in this department, everything charizard has, bowser has a better version of.
CLAWS: 'Zard has 3 per hand, bowser has 4. As well as having more, they are considerably bigger, and on much stronger and longer arms.
TEETH: Bowser's are bigger and in a stronger mouth.
FIRE BREATH: This was a bit of an odd weapon to figure out. They are both very fire resistant...but that doesnt mean fire invulnrable.
The decideing factor here would be the effects on each, and what kind of flame they can produce, which again factors bowser's size.
Bowser is much, much bigger than charizard, so naturally he can produce a much larger/longer flame, giving him more options with it, where as relativley, Charizard has to close in to use his, putting him in danger of bowser.
Having a bigger flame also means charizard has a harder time avoiding it if he chooses to.
ARMOR
Charizard brings speed to the table..where as Bowser relies on his massive size and shell to pull through.
THE EDGE: BOWSER
Yet again, bowser is the better. Charizard may be fast, and able to avoid bowser for a bit, but what can he do to Bowser?
Bowser's girth allows him to shrug off any atack from charizard:
Natural weaponary becomes useless, his scales or shell just deflects the comparitivley small attacks, and leaves charizard wide open.
If charizard tries to drop things on bowser, we'll be nice and give him the lifting abilities comparable to large birds of prey: 1/4th his weight. thats 50 lbs. unfortunatley for zard, 50lbs wont do too much to a 4000lb animal, with a very tough shell.
If he tries to create wind to mess with bowser, it may be the last thing he does. Here's why:
In order for charizard to direct the wind, he will need a way to hover vertically and flap his wings toward bowser with enough force to push air in a significant manner.
While vertical, he can no longer push downwards against air, keeping him in flight, meaning he will plummet.
Even if he were to manage to float, he would only produce winds strong enough to keep him afloat...which will be a light breeze to somethign as big as bowser.
SKILL
Charizard is a Pokemon, and as such spent a lifetime battling other monsters. He has battle-ready reflexes, and has most likely remembered some strategy from his trainer (if he had one)
Bowser hasnt really been known to need to fight anything, other than the occasional Italian stereotype.
THE EDGE: CHARIZARD
Charizard takes this round, Bowser simply has no real fighting experience to speak of. That being said, hes never NEEDED it...
PHYSIQUE
Charizard comes in at 5 foot, 7 inches, and 200lbs. He has large wings, a long neck, long tail and large feet, yet scrawny arms.
Bowser is an impressive 10ft, 4000lbs. He has very muscular arms/legs, a massive head, and a huge spiked shell.
THE EDGE: BOWSER
Bowser takes this round easily. Being 20x heavier is nearly ever a disadvantage.
On top of that, he has no real disadvantages to his design: he has spines/horns protecting his SHELL, and formidable claws and teeth to protect his front.
Charizard on the other hand has scrawny arms, and a long thin neck to worry about in a fight. Not to mention his large wings, which would eb an easy target while grounded.
SYNOPSIS
This fight is regretably very, very, very lopsided.
Seeing as there is near nothing Charizard can do to actually inflict damage on bowser, let alone kill him, and bowser can finish off charizard rather easily....
999/1
Why the 1 you may ask? In 1000 encounters, 99% of the time, Bowser would simply demolish Charizard, or wait it out until Charizard tires, or makes a mistake.
In one fortunate match however, Charizard should be able to hit and run effectivley enough, without getting hit by bowser to end the fight by 1000 cuts, so to speak.
In the end, Bowser is simply too big for Charizard to tackle.