>>37993069zard shitter here
sylveon, like every stall deck, loses to charizard unless the charizard player is a retard and/or just dead draws completely
sylveon gets one-shotted by attach + ability + choice band, wonder labyrinth doesn't help you.
your best shot is playing aggro and abusing guzma to kill off charmanders and charmeleons if they're having to use beacon to salvage a bad start and keeping an eye on what resources they use.
otherwise, plea GX when they already have used two rare candies will set them back a while and you should be able to take a few KOs in the meantime. if they had a charmeleon alongside those two charizards you're pretty much done for though
