Actually there is༺ a method to attack first. By using the misty support card, going first is actually better for the starmie ex deck as if you can get at least 1 energy on staryu on the first turn, you have the potential to access starmie ex 90 damage attack on turn 3. This means that going first with starmie ex deck would potentially beat any deck including pikachu ex, assuming you get both misty and staryu 1st turn and starmie ex at least on 3rd turn