This is more of a core than a single set but I believe that it will be very effective in the next gen metagame and I personally will be running it on most of my teams.
Hydreigon@Choice Scarf
Ability: Levitate
Nature: Timid/Modest
EVs: 4 HP/ 252 Sp. Attack/ 252 Speed
-Draco Meteor
-Fire Blast
-Dark Pulse
-Surf/ U-Turn
Aegislash@Leftovers
Ability: Stance Change
Nature: Adamant
EVs: 252 HP/ 252 Attack/ 4 Defense
-Iron Head
-Sacred Sword
-Shadow Sneak/ Shadow Claw
-King's Shield/ Swords Dance
Don’t worry; those goose bumps will go away in a second. Yes, your eyes do see this correctly. These two Pokémon have absolutely perfect coverage together. Their types coupled with Hydreigon’s ability complement each other in a way that can be viewed as an offensive rebirth of the Jellicent/ Ferrothorn core in gen 5. With the new mechanics and its typing, Aegislash is left weak to both ghost and dark along with ground and fire, all of which is resisted by Hydreigon. And on the switch in of one of the biggest competitors for gen 6, Mega Gengar, Hydreigon takes only {247-251} damage (assuming max Sp.Atk), outspeeds with the scarf(with either timid or modest nature for Hydreigon), and does about 70% with a dark pulse. Sounds pretty awesome correct? But it doesn’t stop there. Let’s say you 2KO that mega Gengar and you’re celebrating your ass off “Yay, I demolished your Mega Gengar and I’m still packing my Ampharos with Fabio hair!” But then, he sends out a Surpluff ready to avenge his fallen comrade. Well easy solution, send out that Aegislash to tank to resisted fairy type attack off of base 150 defenses and you’re ready to retaliate with Iron Head. There are some much to be said about this game changing core, so much so that I cannot cover it all my self so I shall Baton Pass to the rest of you all to give your thoughts about this powerhouse of a duo.