(It seems I'm late to point this out due to typing for so long, but...) First off, about Devolution Spray, if it's anything like the one in Base set or even Hyper Devolution Spray in Neo Discovery, it says you choose one of YOUR Evolved Pokemon, not your opponent's Evolved Pokemon.
Trust me, I was scared too for the same reasons that Broken Pokemon EX listed. (180 HP Basics with their own Stadium, Tool, AND Energy.) So unless there's a change in text that DOES affect your opponent, there's nothing to fear. Hopefully this is more like Hyper Devolution Spray because THAT doesn't discard the evolution card. And since this affects YOUR Pokemon, I can see a few uses for this. There's pesky status conditions that can get removed by this. There's also the ability to reuse those Abilities that say "Once during your turn, when you play [this Pokemon] from your hand to evolve one of your Pokemon..." The cards that come to mind are the new Roserade and Ninetales, and Amoongus; and even though it depends on a coin flip, Shiftry's also a possibility. So you could use the effect one turn, and the next turn, use Devolution Spray and use it again. OR, if you already have a second Vulpix/Roselia/Foongus/Nuzleaf in play, you could use it again that same turn. And the last possible use (that I can think of) is a bit situational. Let's just use... Reshiphlosion for example, I guess. Let's say you have both a fully evolved Typhlosion (you evolved using Quilava, not a Rare Candy) and a Cyndaquil on the Bench. You get a Rare Candy without any way to search for a Typhlosion. Well, if you also have a (Hyper) Devolution Spray, you could devolve Typhlosion back to Quilava, and then use the Rare Candy and evolve Cyndaquil into Typhlosion. (The advantages of that are being able to use a hand refresher without getting rid of the Rare Candy and possibly getting the Typhlosion you need in those cards you drew, and also, if anything you're going against is sniping, both Pokemon probably have a better chance of surviving now.)
Also, would devolving effect Abilities that say "Once during your turn (before your attack)..." and allow you to use that Ability a seoncd time? Like, the one I'm the most curious about is Chandelure (assuming Trainer lock isn't an issue), but I'm sure there are others that would be useful IF devolving did reset the effect of "once during your turn". Again, not sure about that, but I'm curious.
So moving onto the other cards, Garchomp looks really good! Especially paired with Altaria. Quite honestly, I'm not sure how devistating discarding 2 cards from your deck actually would be. (Unless, of course, you're going against Durant.) I mean... I know there's a difference, but it seems a lot of people like all those cards that discard stuff (usually from the hand) in order to do something. (Juniper, Junk Arm, Sage's Training, and Ultra Ball.) Again, I know there's a difference between choosing what's discarded and not knowing what's discarded, but still. Also, in my opinion, wouldn't Garchomp's second attack only be used once against the defending Pokemon, then you'd use the first attack? (Assuming they didn't switch or something.) I just don't think it'd be used as often as the first attack, so its effect shouldn't be that devistating.
On top of Garchomp being nice, Gabite's really nice too. Basically, it's Sunflora (HGSS) for Dragon Pokemon. (And if anyone has used Sunflora, you'd know how fast you can set things up.) Roserade's Ability is nice as well. How often have you been in a jam where you at least just needed this ONE card? Well, Roserade will get that card for you! (Should it be used in all or most decks? Probably not. But it's a nice tech.) And I would argue that if its Ability is indeed the same as Lurxray GL Lv.X's, Ninetales is actually a little bit better (as far as the Ability goes). As long as it doesn't say Ninetales has to be Active, you can just sit it on the Bench and even (Hyper) Devoltion Spray it to use it again another turn. And last but not least, Hydreigon. As a Pokemon, I love Hyreigon. But all the cards so far have only been on the verge of being really good, but in the end, probably aren't. I mean, there's the Ability to move Darkness energies around, which would be nice in Dark decks, but that's a Stage 2 as a tech. Not sure how useful that is. (Pair it up with Darkrai EX?) And the way I can see the other one being okay is for the first attack with Altaria on the Bench, assuming petertclo's translation is right. (Dealing 60 and healing 60? Sounds pretty neat.)
Oh! And I sort of skimmed over it, but of course Altaria sounds great! The way it's worded right now, it sounds like the Ability stacks.
