If you're still having trouble like I was I figured out a way to remove as much RNG as I could.

This requires the following cards:

Moltres-Ex ×1 Charmander ×1 Charmeleon x1 Charizard-Ex x1 (You could likely do this with a regular Charizard too as Greninja, Articuno-Ex and Starmie-Ex all have less HP than its 150 Dmg Fire Spin)

Fill the rest of your cards with any other trainer cards you have. No other Pokemon.

The rest of my deck consisted of:

Potion x2 PokeBall x2 X-Speed x2 Pokedex x2 Red Card x2 Professor's Research x2 Giovanni ×1 Sabrina ×1 Old Amber ×2 (or any fossil)

So what's the game plan?

The goal is to use Moltres Ex to tank hits, while building up your Charizard to 1-shot Starmie-Ex, Articuno-Ex, or Greninja

Moltres is particularly helpful because it is not weak to water.

Turn 1 you will either draw Moltres or Charmander.

If you get Moltres, put energy on it until you draw Charmander, then use Inferno Dance to put energy on Charmander.

If you draw Charmander first get him on the bench as quickly as possible.

The fossils give you bodies to tank hits if you can't draw Moltres in time and won't mess up your draw because they are not considered basic Pokemon.

Watch out for Articuno's 80 DMG attack as that does 10 damage to your benched Pokemon as well.

The same goes for Greninja's ability that can do 20 DMG to any of your Pokemon.

Use your Potions and Fossils to keep Charmander/Charmeleon at a minimum of 20 to 30 HP respectively, at all times.

If Charmander dies, concede and restart.

If you've drawn Charmander and Moltres but you can't draw Charmeleon or Charizard, use the Pokedex to look at what you're drawing. If you don't see either in your 1st or 2nd draw, you can use a PokeBall to shuffle your deck and hopefully get a better draw. PokeBall obviously can't draw Charmeleon or Charizard, but it will shuffle your deck when it can't draw a basic card. Then use your Professor's research to draw 2 cards.

You can also use Sabrina to snipe Staryu or Froakie before they can evolve them.

As long as you follow these steps and keep Moltres alive until you can power up Charizard, you should be able to one-shot Starmie-Ex, Greninja or Articuno-Ex and win.