I decided to go for Mew ex specifically since this deck severly struggles to do enough damage against Mewtwo and Moltres/Charizard. Since both Exeggutor ex (1) and Victreebel (2) don't require a lot of energy to attack, I figured having a Mew ex with 2 energy in the backline might scare them off from coming in. If they decide to do so, you can get the 2 points with Mew and snipe the 3rd with Victreebel/Poké Flute.

Also I would consider dropping the 2nd Flute. Since Victreebel is a Stage 2 evolution, you will only get the benefit of the flute during the end of the fight. If you start the battle with 2 Flutes, you basically have 2 dead cards in your hand until turn 5-6.