Remember, you can only have 1 mega-evolution per-team. Now, if you mega-evolve Charizard, 3 of your Pokemon are weak to Ground.
You can solve this by getting an Ice Type. Since you already have mostly sweepers, you need a sturdy Pokemon your team can fall back on.
Avalugg @ Leftovers
Ability: Ice Body
EVs: 252 HP, 252 Def, 4 Atk
Nature: Impish (^Def vSpAtk)
Earthquake (Covers 3 of its weaknesses)