This post will contain the compiled deck list thus far and will be periodically updated. To make sure you're always up-to-date, make sure you're following the discussion. Don't rely on this post when making your suggestions.
This card is great to fill up the bench slots needed to power Emerald Break, and can also refresh your hand to allow you to acquire even more basics to bench. Overall, a great consistency card that can be easily searched out with Ultra Ball or Winnoa (if they are added).
I'll add 1 more DCE, as having 4 increases the odds of drawing them and means we can use them 4 times if we decide to not include Lysandre's Trump Card.
I'll also add 2 Mega Turbo. With Shaymin-EX, we'll be drawing plenty of cards, and we will likely use Ultra Ball to thin our hand to use Shaymin again. So, with this we can speed up Rayquaza even more.
I'll sweep in from the side with some techs. While M-Rayquaza-EX is powerful, he has a few limitations. One of them is Safeguard. Having all that power doesn't help if your target is immune to Pokemon-EX! A small Raichu line seems like a good choice, as it only needs a DCE to attack, and operates off the number of benched Pokemon, much like Rayquaza. Even if Sky Field is countered, a bench of five Pokemon will do 100 damage with Circle Circuit - enough to Knock Uut a Suicune PLB or Sigilyph DRX / LTR. It can also one-shot an opposing Rayquaza in the mirror match in the off chance they can't get an Altaria out, and is a nice choice of attacker if you can Lysandre and one-shot a Shaymin to win the prize trade.
After testing, Jirachi-EX is also a nice tech. It seems to have been left by the wayside by some players in favor of Shaymin, but Jirachi's instant search for a Supporter is great for consistency. It's almost like having five Shaymin-EX in your deck!
I am going to add 1 Shaymin EX from Roaring Skies, as has been said earlier, this card helps set up this deck very fast if you are able to leave only a few cards in your hand. In addition, I will add one Swablu and one Altaria from ROS (the Altaria is the colorless one as well). Altaria's ability removes Rayquaza's weakness to Lightning, allowing potential threats such as Manectric EX to be better handled. In addition, it also has the Delta Evolution Ancient Trait, meaning that it can be played on the same turn Swablu is put into play, which can help with playing more cards from your hand for Shaymin.
Four Ultra Balls in this deck is a must. That's your ticket to more Shaymins.
Now for something a little unorthodox. I don't think Computer Search is the best ACE SPEC for this deck. Yes the consistency it provides is unmatched, but with the ridiculous amount of draw power that Shaymin combined with Sky Field give, you are extremely likely to draw every card you need unless you are very unlucky. That said, an easy way to recycle Shaymin is Scoop Up Cyclone. Unlike SSU it requires no coin flip, and it doesn't take away your Supporter for the turn a la AZ.
+1 Ultra Ball
+1 Scoop Up Cyclone
-1 Computer Search
I'll add 2 Exeggcute (PLF 4/116) and 1 Skyfield. The Skyfield is to allow for more benched Pokemon, and the Exeggcute are discardable benchmark sitters who you can easily get back if Skyfield (and therefore some benched Pokemon) are discarded