Here's my input at first glance:
The first thing I noticed is that you split the defensive EVs between Def and Sp. Def on your Magnezone. Run 252HP Evs instead, since this will give you more bulk. Also, Tri Attack won't accomplish much since it doesn't get STAB. I would suggest putting Thunder Wave over Tri-Attack unless you have Hidden Power Fire or Ice.
If you're using Mega Sceptile, don't use Charizard. You should only be considering Mega Charizard, since in OU there are many better options than regular Charizard, such as Talonflame or even Moltres to be frank. A Swords Dance Mega Sceptile is a reasonable choice in OU, though a Jolly nature might've been better for Pokemon such as Mega Lopunny.
I'm really wondering what's going on with that Umbreon; that's a very unusual set you've got there, and I don't think it'll work out that well either. To make a long story short I would switch it out, for either an offensive pokemon or physical wall such as Gliscor.
Your Sylveon only wants to take Special hits; Rocky Helmet won't do a good job at deterring physical attackers, so you'd be better off using leftovers.
