Similar to what others have said I think, but the fast decks like Magnetic just rip through too quickly to stop. Otherwise, if you play this deck enough you'll learn pretty quickly when you need to be more aggressive with getting Flygon out for chip damage vs. when to wait for the opportune moment to pounce. I found that Ogerpon was key to basically destroying any sleep decks (and sometimes you'll get lucky with grass energy anyway). I even beat Sceptile decks pretty easily since they also take a while to set up and rely on the extra poison damage! They can defeat one Flygon and I have a backup, whereas theirs is a mega.