If you know how good this card is, then you know that theres many ideas floating around on how to load up Mewtwo-EX as best as possible. At the moment i know of two very good sounding methods of loading energy for its first attack.
Eeletrik is one of those methods and has these pros and cons:
Pros:
+can recover energy from the discard and would make the deck quite consistent.
+stage one so relatively quick set up.
+can be easily searched.
+decent typing.
Cons:
-make for a turn two set up (without pachirisu) making it slow.
-low hp and high retreat cost making it catcher bait.
-only attaches to the bench.
-requires a handful of different cards to ensure a decent set up.
Another of these energy acceleration is Celebi Prime:
Pros:
+basic so can be searched for with cards like collector.
+able to ensure turn 1 attacking with Mewtwo-EX of at least 60 (with one DCE attached).
+low retreat cost of 1 and can be reduced to zero with skyarrow bridge.
+needs a low cost of additional support cards.
Cons:
-has to active to use Poke-Power.
-low hp for a non evolving basic > making it catcher bait.
-gets 1HKO by nearly everything in the format.
-bad weakness.
As you can see, they both have their pros and cons in terms of energy acceleration and are equally good with Mewtwo-EX. Some alternative ideas for energy accelerating is in the forms of slugma UD, Emboar BW, Eletrode Prime, Pachirusu CoL and Jirachi CoL/UL. Most of these would need to be used with shaymin UL as otherwise no energy would get to Mewtwo-EX. One other thing i am unsure about is whether to run any tech in the deck other than the energy acceleration. I have heard some people saying to run Zekrom-EX with Eeletrik as an alternate attacker but i cant think why you wouldn't just run Zekrom-EX with Mewtwo-EX as a tech.
on a side note, this might sound like a nOObish question. With the new EX's could i have 4 Zekrom and 4 Zekrom-EX??? Thanks for answer to this question!!
EDIT: added Mewtwo-EX image, Zekrom-EX and "removed" my noobish question