Not sure if I agree with no Shaymin, but its worth a try. A tech of just 1-1 sushimaster seems low, but again, would need tested. I agree with cutting down on some things, but I want you to try something for me.
-1 Teammates
-1 Sycamore
-2 N
-1 Dimension Valley
-1 Level Ball
+3 Battle Compressors
+1 Skyla
+1 Delinquent
+1 Hex
I feel a tech of battle compressors would work well in here and here's why. Whether you use skyla for one, or happen upon one from Trainers' mail, you give yourself the ability to shorten your deck to just the cards you want to pull, as well as setting up all the trainers you want when you want them in your discard pile. The ability to VS seeker your teammates, Sycamore, Team Flare Grunt or Hex at any time via VS seeker is such a nice tool to have. This is especially essential if you're going first and run against Toad or Vileplume. You want to discard that Hex and pick it back up with a VS seeker since the majority of your tech is item cards. Your strategy will vary game to game depending on what deck you play against. Against Vileplume, you want Hex and Delinquent in your hand at all times so you can discard their stadium as well as Hex if you need to, but if you're setup to mill then it should be an easy matchup as they will already mill themselves down. Toad I wouldn't worry about because your tech sets you up to discard the DCE or lysandre out something else like Hoopa, Shaymin or whatever else makes it difficult for them. NM again is easy because they will mill themself down faster than take prize cards. Since you run 4 puzzles there's other things you can go less of since you have the ability to get anything back, plus with bunnelby's attack as well. Bats/Trevenant will be scary decks to face. Granted a simple Hex will take care of them initially, but Tree Slam will hurt and your dimension valley helps them as well, so consider just using Bunnelby's attack for 1 so that you dont help them out.
You may be right with Sushimaster, however..the deck spots are slim..so even fitting 2 Shaymin in can be an issue...
With Sushimaster, every creature can be tutored with Level Ball, and I think given the decks nature...and potential small numbers of shaymin/octillery, having a constant source of cards, as opposed to a one time thing..nothing to re-use Shaymin, is potentially much more beneficial..Shaymin isn't always strictly better.
I agree, like the post before, with the addition of some tech cards like Hex/Deliquent/Xerosic and such could be very beneficial. Trimming some numbers on cards that maybe aren't as required..Bridgette for example.
I felt it was a really solid base to work from though...
I haven't actually built the deck yet, but I've managed to trade for some Mew's, so, I'm going to have to now...I'm invested XD