I've too built and run this deck and offer the following thoughts/comments from my experience:
M Gengar EX is really not that more effective than Gengar EX.
M Manectric EX has been useful rarely for energy attachment acceleration (due to lots of F decks being played in my area).
4 VS Seeker are excessive IMO, especially if you are also running Lysandre's Trump card too.
Why no Energy Retrieval to help get needed energy from your discard pile?
A 1-of Sigilyph and Wobuffet are in sufficient. What if the 1 is prized?
4 Ultra Ball are excessive, IMO. Should you be Item-locked, then you won't be able to play any of these.
Playing a Battle Compressor early game in order to discard a Supporter that you can retrieve later via a VS Seeker can be useful. But, I do think devoting 2 deck slots for this Item is again excessive and would have lower priority to some other needed cards, IMO.
Why no Stadiums to counter opponents' Stadiums?
Why no Tool Retriever / Xerosic to remove Tools placed upon your Poké?
Given the above comments, I'd suggest the following changes:
-1 M Manectric EX - 1 should be sufficient to help protect your Gengars.
-1 M Gengar EX.
-2 Mewtwo EX - too situational and becomes a liability as soon as you attach 2 energy; so, not that effective in this deck. Plus, the DCEs are needed for your Gengars, Kyurem, Reshiram...
-2 Battle Compressor
-1 VS Seeker
-1 Ultra Ball
-1 L - 3 L energy should be sufficient
+1 Sigilyph
+1 Wobuffet
+1 Energy Retrieval
+1 Pokémon Fan Club
+2 Virbank City Gym - without a counter-Stadium, Yveltal EX can just 1HKO your Gengars when Shadow Circle is in play without concern for a KO response from you.
