That definitely pertains to me considering I'm a Charizard main. Until I learn the character more thanks to videos like yours, I've been starting a lot of combos off reads into grabs, but my favorite move is Up Smash with Charizard. At low percents it combos, starts nice juggles, the works.
I also like using Seismic Toss at medium/low percents and following it up with a glide attack or FAir since it's the perfect percentage to knock someone off the stage and proceed to breath fire on them for the KO. My favorite moves with Charizard are Heat Wave and USmash I think. But there's so many options with him!
Thanks to his shield, he can afford to take a beating from rushdown shining from characters like Falco and the like. If he didn't have that, he'd be screwed.
My favorite damage-building combo though, which works best on Battlefield is starting on the left or right platforms,
Opening move (can be Jab, DAir, DSmash, whatevs) -> Seismic Toss -> Glide attack to upper platform -> USmash -> UAir/FAir/BAir/NAir follow-ups
Using the glide attack to the upper platform, you actually cancel out the last part which delivers the knockback, locking them into the fire and letting you immediately perform an USmash. I have yet to see if this would let me grab or not, but with Charizard there's so many options.
Charizard is the reason why I play P:M.
I wanna help advance his metagame and when this game takes off in the full version, I wanna become one of the best users of him. It's gonna be fun.