The concept here is to use Blastoise to Rain Dance a ton of water energies onto your water-type Omanyte before evolving into Omastar and using Spike Barrage for a horrific amount of damage.
Misty's Tears help accumulate water energy into your hand quickly, and Cleffas and Mantines buy you some time in the early and mid game while you gather the right evolutions.
Ample amounts of Switches to ensure your Blastoise is able to stay on the bench safely.
Once you have a couple Omastars and a Blastoise, get your Aerodactyl going to prevent your opponent from evolving to ensure a juiced-up Spike Barrage is doing lethal amounts of damage.