I'm seeing a new spin on an older gaming strategy with MegaGengar, "DragTag". I didn't read all the comments so I don't know if someone had suggested it, but the idea is now to take steel types out of the equation (somewhat) and replace Magnezone with MegaGengar.Here is the set I would use:
Gengar @ Gengarite | Shadow Tag
252 Spd / 252 Sp.Atk | Timid
Shadow Ball | Sludge Bomb | HP Fire/Focus Blast | Calm Mind
I'm sure all of you know what a DragMag Team is, this is simply a re-imagining of it. The idea is to trap steel types and Fairy Types with MegaGengar and dispose of them. This would allow dragons to Wreak Havoc. Sure, a lot of Dragons get steel coverage moves to deal with Dragons, but not all of them do. And even then, you may have a few choiced dragons in your group, and you don't want to waste a turn going through and switching out (and maybe back in) with a nearly full dragon team when there are fairies rampant. Mega Gengars massive 170 Sp. Atk, along with Calm mind give him enough power to take out steel types with HP Fire, along with added protection against those pesky Fairy Types (correct me if I'm wrong but every fairy type move in this gen is specially based other than Play Rough, which against Gengar is a resisted hit anyway.) You could use focus blast if you want to, but I opt for HP fire so you have at least Neutral damage against fairies with all 3 moves.