Hm, an interesting deck idea here, Shaymin! I do think there's a few techs included here that you really don't need, and you'll free up some space for techs that would of more use to your deck.
Take out: (15)
-1 Shaymin-EX
You actually don't have enough Bench space to be using this many Shaymin and Tapu Lele. You would want to have a Shedninja in the active, and a Shedninja and 2 Ninjask/Nincada on the Bench, so that you can constantly stream Shedninja. That leaves very little space for you to play your Robo Subs, let alone your Shaymin and Tapu Lele, and so a combined total of four is overkill. Additionally, the more EXs/GXs you have, the more fodder your opponent has to Lysandre and kill. Plus, you don't actually need to draw through your deck that much. No, they are not a good reason to run Skyfield - if you need Skyfield, then you are playing wrong.
-1 Tapu Lele-GX (See above)
-1 Ninjask (You also don't need this many Ninjask, because you'll be shuffling in your Shedninja/Ninjask via Sacred Ash regularly. Removing a Ninjask will declunk your deck and make it more efficient.)
-2 Ultra Ball (We can use this space better. After all, Level Ball can fetch your attackers easily.)
- 1 Lysandre
We need to use this space better. VS Seeker means you can reuse your Guzma anyway. Why Guzma over Lysandre? Guzma is a great backup in case you get Lysandre'd (for example) and need to Retreat your Pokemon but don't have the Energy. If you have the Active you want up front, you can just switch into Shedninja and retreat back into your ideal Active. Easy peasy.
- 1 VS Seeker (That's... a lot of VS Seeker. You won't need that many, so let's use this space better.)
- 1 Super Scoop Up (You either need to run 3 of these, or not at all. One is not going to do much for you. I suggest taking this out, because I think the Devo Sprays will work fine for you, and we need the space for better techs.)
-1 Sacred Ash (This needs to be a Super Rod or Stretcher, because you need to have one or two Shedninja on your Bench at a time. That means that you'll rarely ever have above 4 Pokemon to shuffle back in; nothing your Super Rods/Stretchers can't handle.)
- 3 Sky Field (Not an optimal Stadium choice.)
- 2 Counter Energy (If you have more Prize cards remaining than your opponent, then you are playing wrong. Plus, you shouldn't ever be using your EXs/GXs anyway, because they'll be KO'd in return.)
-1 Life Dew (I do not think that this is the best ACE SPEC choice, since if you're executing your strategy right, your opponent should be attacking Shedninja/Robo Subs.)
Put in: (15)
+3 Level Ball (for consistency)
+1 Prof. Kukui (You need as much damage output as possible. This Supporter is great for whenever you don't need to use an N/Sycamore/etc. Providing you have this or your Stadium and a Choice Band, you'll be able to hit those important 2-hit KO numbers.)
+2 Team Magma's Secret Base // Virbank City
You need to maximise your damage output for this deck to be viable. Team Magma is fairly reliable for some one-time blanket damage. Virbank City is the ideal, but it takes up quite a bit of space and is expensive. I would suggest Po Town as it'll be great against Evolution decks, especially GXs, but because you're devolving a lot, you might find that you'll KO your Ninjask instead.
+1 Computer Search // Dowsing Machine // Scoop Up Cyclone
Computer Search and Dowsing Machine are great for consistency, the latter might be more useful since you need to be recycling your discard pile a bit. Scoop Up is a versatile way for you to reuse your Ninjask to get another Shedninja in a pinch, or can be used to get a Shaymin/Tapu Lele out of the ring.
+4 Puzzle of Time (You are recycling your discard pile quite a bit, which makes this a great consistency tool.)
+2 Stretchers (Sometimes you'll need Pokemon to go directly into your hand (e.g. Ninjask), which is why this is important. It also gets out Shaymin/Tapu if you need it.)
+1 Rainbow Energy (In case you ever need to use Cursed Drop. The extra damage counter isn't a problem, since your Pokemon have low HP anyway. You could also do with 1 more Energy.)
+1 Bridgette // Robo Sub (Maximise your chances of Bridgette early game or have a more consistent Robo line.)
NOTE: If you're running Lasers, remove 3 in any combination of Bridgette/Robo Sub, Rainbow Energy, Stretcher, Super Rod or Devo Spray. None of these are necessary for your deck to run, but will help your consistency.
Honourable Mentions:
Kartana-GX // Tapu Fini-GX (Both have some usable GX attacks that could be worthwhile, especially if you swapped a [G] Energy for a second Rainbow Energy. Kartana can secure that last Prize card in a pinch - and Stretchers mean it can be in your Discard - while Tapu Fini-GX is more situational, but could be useful if you've got a particularly nasty Active up front.)
Another Prof. Kukui (Consistency!)
Skyla (A great tech when running Puzzle of Time. Being able to find whatever Trainer you need can be highly useful in a pinch.)
Hoopa SL // Mew EVO // Wobbuffet PHF (Great walls, but because you're not running Float Stone or Switch, they aren't too viable.
EXP. Share // Wishful Baton (You might find that you're not attaching Energy as much as you need to, and this will patch those holes.)
