Idk what to tell you for this specific match up. I don't really have trouble fighting charizards, not like you'd often find one anyways. But since i happen to play both these characters, i would say just try to stay away from being above him, as there's no hope in over powering his up tilt for mario, or any character i believe. Be aware of charizards rock smash, especially when going for the uptilt combos. Im pretty sure he can use it immediately if you try this at 0 percent. Also be careful on fireball usage, because he could just flare blitz through them. Try to distance yourself and find openings, because charizard has much more range than mario, and can just space you out with his d-tilt or even his jab. One thing to watch out for is charizards jab, which does 12%, and at kill percentages, his jab 2 can combo into fly, which a good charizard will surely try to abuse. He also has a kill throw which im sure you're aware of, so at around 120ish percent try to avoid being grabbed at all costs because if it's fresh that's pretty much a guranteed kill. Also another thing to watch out for. When charizard down throws you should almost always jump. If you air dodge there's a hugh chance you could be frame trapped. When playing a couple opponents as charizard when they dodged my fair if i FastFall i could almost always get them with my jab, which at low percentages leads into another fair. At that point they could either get hit or frame trapped again. So try jumping as it's your best bet. You should also keep wall jumping as an open recovery option, but be aware if you become predictable a charizard could try to dair you. Also if you happen to get trapped by his flametrower off stage, don't frantically tap up b, as you'll most likely land on srage and be open to a forward smash, which will most likely result in a lost stock. You'll want to fall down a good distance where you can up b and auto snap on the ledge, but be aware you've most likely been hit out of your second jump. Also i would advise against heavy offstage edge gaurding of charizard, as his recovery options have super armor. That is unless, let's say you're at a low percentage and you sent him pretty far off the stage, you could try eating up a flare blitz to the face in order to gimp his horizontal recovery, or possibly put the charizard in a bad position. But if he saved his jumps this tactic would pretty much be useless. Idk what else i could say. Sorry for the long response.Hope some of this information helped though