Try this team:

Charizard-Flamethrower, Fire Blast, Overheat, Blast Burn.
Blastoise-Surf, Ice Beam, Hydro Pump, Hydro Cannon.
Venusaur-Sludge Bomb, Solarbeam, Giga Drain, Frenzy Plant.
Zapdos-Fly, Drill Peck, Thunderbolt, Thunder.
Mewtwo-Psychic, Psych Up, Metronome, (Your choice)
Dragonite-Dragon Claw, Flamethrower, Outrage, Hyper Beam.