Set up quicker than they do while disrupting their Beacons with N. That's really all you can do. The advantage you have over them is that you only need one Gardevoir to start taking KOs on T2. They need a minimum of two Metagross as well as two Energy in the discard pile in order to attack T2. You need six Energy to OHKO a Metagross with three Energy on it, which can be difficult to do.
Espeon-EX is a bad idea. In order for it to be effective, you need to do at least 90 damage. That means you had to have swung on the Metagross with Gardevoir. And if you swung on a Metagross, it is probably going to OHKO you. So you then bring out Espeon and devolve the Metagross you hit. It's an uneven prize trade. You also run the risk of getting Espeon-EX OHKOed by a banded Metagross next turn.
Some Gardevoir players have started teching in Turtonator-GX. The Shell Trap attack damage is negligible; that's not why you're running it. The idea is that by hitting you through the trap, they will have 80 damage on them going into your turn, circumventing Max Potion shenanigans and making it much easier for Gardevoir to secure a KO (you only need three Energy instead of six). So you could try that.
That's a bad idea, not the least reason of which is that you fall 10 damage short of a KO, even with a Choice Band. Further, the deck revolves around tanking hits with Metagross's huge HP. Gardevoir has to commit a ton of resources just to take a single OHKO, while you can recycle your Energy easily and take the revenge KO. Metang can do none of these things. You can use Dhelmise to nick that last bit of damage, but the deck struggles enough with Bench space issues.
The only time you should use Metang is against baby Alolan Ninetales.
