IMO, you should run a Magic Bounce Espeon, Sync. isn't that reliable, also with MB you can force switch hazard setters while you set up your own Reflect. Same thing with Mamoswine, if you're not using a Hail team, there's no reason to be running Snow Cloak, since Thick Fat mitigates a bit that Fire weakness while weakening Ice types as well. For the Garchomp, instead of Brick Break, why not Poison Jab or even Iron Head? if you have the time to breed another Gible that is. I haven't tested Mega Banette yet, but since Prankster doesn't activate the turn you mega evolve, maybe you should run Protect over Taunt to ensure you don't get OHKO before you can even attack. The Jolteon looks great, but lacks coverage... So If you can manage to breed one with Hidden Power Ice, or even Bug, I can tell it would be a lot better. Anyways, it looks like a well balanced team, with some weakness to Ice and maybe ground, but great regardless.