As a Stage 1 with a two energy attack that deals 90 damage, Starmie ex has one of the most efficient attacks in the game. If you are going second and have both a Staryu and Starmie ex in hand, you can deal 110 damage by your second turn. That's enough to knock out the vast majority of Basic and Stage 1 Pokémon.

In the game where the stars don't align like that, the rest of your deck can still carry you to victory. By leveraging Misty or Manaphy to generate additional Water energy, you can accelerate into Palkia ex's Dimensional Storm attack and start pressuring your opponent's Active Pokémon as well as their Bench.