A little math:
3 Decidueye-GX Ability uses(6 damage counters)+ 1 Zen Force use(6(from Decidueye-GX ability use)*30)=60+190=250: the maximum amount of HP a currently-printed Pokemon card has ever had(meaning until something is printed that goes beyond 250, which is not in the near-term, 6 counters from Decidueyes is barely enough to 1HKO anything, and in case of resistance, you can always include Kukui in deck, just in case), including GXes[/math]
^ If the above is true, then I'd say, assuming OP decides upon the above deck, since a lot of these cards will more than likely to be rotated out, assuming the most likely: BKT-On, the list of such cards include: FoGP(first-and-last printed in Ancient Origins), VS Seeker(first printed as a regular card in Phantom Forces, last printed as a Secret Rare in Roaring Skies), Trainer's Mail(first-and-last printed in Roaring Skies, and reprint doubtful, as it is likely that its upcoming reprint in Battle Arena Deck 2017 will KEEP the Roaring Skies set symbol, which will mean its rotation clock will NOT be reset) Hex Maniac AND Lysandre(both last printed in Ancient Origins), drop the ones likely to rotate, 1 of each of the Decidueye-GX line, and finally, 1 of each of the Alakazam-EX line(including spirit link), then add the following:
2-2 Rockruff/Lycanroc-GX(to replace Lysandre come Guardians Rising's release, as its Ability exactly mimics its effect, but since it can only be used when you evolve its Rockruff stage into said Lycanroc-GX...)
3 Altar of the Moone(as soon as Guardians Rising is released stateside)(free retreat for Alakazam-EX and its Mega)
4 Puzzle of Time(last printed in Breakpoint)(replaces VS Seeker post-BKT-On rotation arrival)
3 Rare Candy(evoluton to Decidueye-GX post-FoGP rotation-forced exit)
2 Mallow(to pick out Rare Candies, evolutions, etc., and hopefully, you have 2 or less cards in hand for Oranguru Instruct usage)
2 Skyla(to scoop up Trainers, including Mallow)
1 Brock's Grit(to scoop out your Alakazam-EX line should it get KO'd, as well as replacing the third card of each stage of said evolution line)
2 Professor Kukui(just in case you run into a pokemon w/ a psychic resistance, such as steel-types, psychics, among other damage-reducers)
^ What do you think of my proposals to ensure this is truly the "deck of the future"?
I don't think it is a good assumption that Trainer's Mail and VS Seeker keep the set symbol or don't get some kind of SUM equivalent. At this point, I would rather not speculate far enough into the future to really say what Pokemon will do for some of the more staple cards
Who knows, something better than either might come out or we might get something like an ace spec equivalent. That's generally why I don't like building deck lists using upcoming cards (even for known sets like SUM2).
That said, I think some comments on the deck changes are warranted right? Cuz why not!!!!
I don't like the Lycanroc-GX addition. The deck is already saturated with a couple of heavy pokemon lines that make it clunky. Adding another 2-2 line even reducing the supporter line by 2 isn't going to help this. I get the idea is that we just freed up 4 slots from VS Seeker and another 4 from Trainer's Mail, but TBH I am unwilling to drop them without knowing what is coming because, as stated above, I think there will be something very similar available in upcoming sets.
I am also less than sure about adding Alter of the Moon. TBH, I would look a lot more closely at Parallel City as a way to limit my opponent's options in a post Shaymin / Hoopa world. Less downside to dropping it on them right? That said a 2-2 / 2-1 split might work between the two. Seems like something you at least have to play with a bit to see how much you like the ability to take 1 less off that retreat cost.
Puzzle. Maybe? This is where I am unwilling to commit before I see how the rest of the upcoming sets shake out. I don't see Pokemon dumping the ability to grab supporters out of my discard down to nothing. If anything, given the way they seem to be going by making stronger versions of things and calling them supporters, I could see Pokemon doing something like a supporter that pulls back 3 cards from your discard into your hand. Is it overpowered? Absolutely. Has that stopped them before? Nope. Or maybe a supporter that lets you grab a card from the top of your deck and one card from your discard. I mean, I don't like to theorymon, but I could see either idea happening. But let's say none of that happens, I think Puzzle gets a whole lot more play just like you are suggesting!
Candies. Think they would have to be there. Also think the 4-4-4 line turns into a 4-2-4 line at best. Might even turn into a 3-2-3 line. I played around a ton with Magnezone and absolutely hate having to level my S2 pokemon this way BTW.
Mallow. Cool card. I want to play around with it. I think there is another pokemon coming out that lets you draw a card off the top similar to Slurpuff from Phantom Forces. I don't know if that has a place in this particular deck (unlikely), but it is at least something to look at along with Oranguru for Shaymin replacements. Mallow should have a place in almost any deck I am guessing
I think 2 Skyla is 1 Skyla too many even with the issue of having to hunt down rare candy. I might not agree with this statement in the future if the game does, in fact, shift to a slower format. I will believe it shifts to a slower format when it happens.
I hate everything about Brock's Grit in this deck. If they punt a pokemon, they punt a pokemon. I have played this deck enough now to know that I haven't had one time where I have regretted a bunch of pokemon being in my discard (or energy for that matter) and thought to myself...self, I really wish I had a super rod. Take that sentiment and apply it to Brock's Grit x2 for being a supporter lol!
Kukui is another interesting one that sounds good in theory. Mathmon incoming! Say I have 40 damage on the active then hit for 10+120+40. That gets me to 170. Kukui gets me to 190. Just enough to KO almost any basic without a FFB, so that is good in a lot of scenarios. 50 damage (doable if you hit with Suppression once or hit with the ability when you level to M Alakazam + 1 Feather Arrow) gets you 10 + 150 + 50 which gets many megas and a lot of the new S1 GX mons. Kukui gets that to 230 which finishes off almost all the megas + all the S1 + all FFB attached basics not named Wailord. Another point in its favor. 60 damage = 10 + 180 + 60 = 250 + 20 to 270 with Kukui which amazingly STILL doesn't finish off Wailord! LOL! All that said, I think you might have convinced me to play around with Kukui in the current deck as well as using it in the future deck!
Sorry for the fairly negative response to most of the ideas. I would like to be more positive on them, but as I have said a lot, I am pretty wishy washy on the whole idea that VS Seeker + Trainer's Mail or something like Acro Bike will all be out for good following this season. TBH, I still think they are going to promo at least one of them with new art and SM18 or XY223 or whatever the numbering is. Overall, the deck itself is pretty clunky to begin with and I honestly think it might just flat out die once FoGP rotates along with everything Vileplume in Standard. Going to be real, I think Pokemon needs to start thinking long and hard about some good basics for Grass going forward without FoGP because it looks like a freaking wasteland in Standard for Grass types that don't require some kind of stage up.
Thanks for the input though. Especially Kukui. It really got me thinking about the card and I liked that a lot!