I love Gardevoir and it's practically the only thing ever keeping me in Deck Garage. Let's look this over.
➤ Pokémon
In all honesty, I would drop Eevee and Sylveon-GX entirely to fill the spots with 2 Alolan Vulpix GRI and 2 Alolan Ninetales-GX LST. Instead of spending the end of your turn to search for the cards you need, it's a lot better for your current turn to be able to search for items specifically and keep your turn going. For instance, instead of ending your turn with Magical Ribbon to search for 2 Rare Candy to evolve your Ralts next turn, search for them with Mysterious Guidance and keep playing through your turn with your new Gardevoir-GX, where you may even be able to use Secret Spring that turn to take a knockout against your opponent. Setting up as consistently and quickly as you can is the name of the game for Gardevoir-GX decks, and when you can speed that up, it really helps. (Beacon is also a great starting attack as well, and it can be even used if you don't have energy in your hand. I argue it's actually better than starting Eevee in some cases.)
I'd consider adding 1 Marshtomp to your list, but this is only if you decide to add 1 Ditto Prism Star as well. This means it's a lot easier to be able to get Swampert out if you're unable to play Mudkip, either by prizing them, having them be knocked out or simply never drawing into them. Ditto Prism Star is a wonderful option that should be considered in almost every deck with evolutions for the flexibility to evolve it into whatever you want, whenever.
+1 Tapu Lele
Most decks need Tapu Lele as a starter to pull out a Brigette or Professor Elms Lecture, so you want to try to get one in your starting hand. You could even do +2 if you feel it's needed.
I agree with every word of this.
[-2 Eevee, -2 Sylveon-GX, +2 Alolan Vulpix GRI, +2 Alolan Ninetales-GX LST, +1 Marshtomp, +1 Ditto Prism Star, +1 Tapu Lele-GX]
➤ Trainers
You can easily drop Pokémon Fan Club, since between searching for items with Mysterious Guidance (or even Magical Ribbon if you decide to still play that) you can still play a draw supporter and this card doesn't offer you anything that those effects wouldn't.
I'd advise raising your Elm's count to 2, since it's an important first turn supporter to play, and the likelihood of being able to draw into it or not have it prized is increased heavily after putting in a second copy. This is obviously pure luck, but playing my list of this deck with 2 Elm's, I've started with 1 in my hand in about a third of the games I've played and it helps a lot to not have to bench a Tapu Lele-GX to Wonder Tag for it.
I'd also raise your Cynthia count to at least 3, since it's arguably the best draw supporter we have in the format, and since it's shuffle-draw, it's almost never unsafe to play a Cynthia rather than any other draw supporter in your deck. It's a really good card, so why not play the most you can?
I'd drop all 3 Tate and Liza. If you're playing it for the shuffle-draw, you're going to be drawing an extra card every single time with Cynthia. If you're playing it in order to switch your Pokémon, I'd simply play 1 Switch or 1 Escape Rope, which you can search for with Mysterious Guidance and still be able to play a supporter for the turn.
You don't need Energy Retrieval. If you're running low on Energy in the late-game, use Twilight GX and shuffle in the resources you need to win the game. I'd also say the same thing for Rescue Stretcher, but I honestly think whether or not you play Rescue Stretcher in Gardevoir-GX should be up to the person playing.
[-1 Pokémon Fan Club, +1 Professor Elm's Lecture, +1 Cynthia, -3 Tate and Liza, +1 Escape Rope, -1 Energy Retrieval]
➤ Energy
Super Boost Energy is a very gimmicky card. I like it in this list more because of the ability to play Swampert as well as Gardevoir-GX, but I haven't done sufficient testing with it. If it works, it works. If not, you can explore the idea of removing it and putting in an eighth Fairy Energy.
You've got a nice start. The thing is, I strongly believe Sylveon-GX just isn't a good enough partner for Gardevoir-GX anymore now that Alolan Ninetales-GX is in the format. Playing Sylveon-GX just seems slower when you really need to be setting up quickly and consistently when you play a Gardevoir-GX deck. I think your list is good, but it's just missing optimization and you could be playing better versions of cards you already are.
Test these changes out, and see how they work. Let me know if you have feedback on these changes as well and I'd be happy to discuss them further with you.
Hope this helps!
@Ampharos142
I feel like you have too many trainers and not enough pokemon, so I would suggest adding a 2 Gardevoir SM7 and 1 more Ralts.
While this is true, I'm not completely certain if Gardevoir LST is worth playing. But you probably shouldn't be playing another Ralts, as then you'd be playing 5, haha.
