Every fire breathing reptilian in other franchises are just avatars Charizard uses to interact with the omniverse around him. Charizard is the archetypical fire dragon, he is the concept in its purest form. Charizard resides in a archetypical realm above our plane of existence and he makes sure his likeness exists in every popular children's franchise.

>Draggo from Bakkugan?
That's just Charizard.
>Toothless from Dreamworks?
Charizard.
>Greymon from Digimon?
Charizard interacting with the digital world.
>The Dragon from Shrek?
Charizard if he female.
>Teostra from Monster Hunter?
Charizard
>Bowser?
You guessed it. Charizard manifesting himself across the time stream into a franchise that came into existence even before his own.
>Smaug
You get the point.

Charizard is timeless. Charizard is boundless. Charizard is the blueprint. Charizard IS.