I see, I guess I'll try it first with whimsicott since I won't be attacking in the early turns and that would help alot against aggresive mons until I have one to fight back. Although sylveon looks good too. How's the matchup with other decks if you're using whimsicott or sylveon?
Keep in mind neither Whimsicott or Slyveon, or any other Pokemon you decide to throw in there are really staples of the deck. I've been using Whimsicott this year because Aromatisse rotated but if you play in expanded all the currently "optional" card should be taken out for 2-2 Aromatisse and 3-4 Max potion. Whimsicott has proven extremely helpful should M Gardevoir take non-lethal damage. Additionally Xerneas is your best start and while going 2nd isn't bad at all in this deck you only have a 40% chance of starting with at least 1 Xerneas.
On the topic of Garbodor this deck should do well. If you are truly afraid of the Garb deck and want to go all in to countering it run 1 more break and 2 more energy. Get Xerneas out and only setup 1 Gardevoir. Otherwise play it normal just without using items beyond spirit link and being careful to Sycamore away items. The items are not the staple of this deck but rather cards used to speed the deck up and make it more consistent. Drampa is good into Xerneas as it's second attack will 1 shot Xerneas and it's Break if it gets the +80 so build up Gardevoirs specifically for that. Imho, easy matchup and definitely in your favor.
Favorable Matchups:
Garbodor
M Mewtwo (though that deck is only slightly favorable as it's very much a game by game type deck, but it's hard still to get a 1 shot with M Mewtwo)
All Turbo Dark and Yveltal Decks (resist 20 makes all their attack 20x rather than 20+20x)
Slower Energy Stacking decks (Xerneas is very consistent, beats out Turbo Dark, Volcanion and other energy ramp decks)
Denial Decks (Ability, Item, Supporter locks and energy denial are not great against this deck as it relies more so on the tempo of it's attacks and should run energy restore cards, imho this is one of the strongest features of the deck). Slyveon Deck is still annoying regardless, just try to keep an energy in hand and continually setup with Xerneas, they will run out of counter cards before you run out of energy restoration, I've played against it enough, though the matchup is favored to Sylveon.
Decks based on reliable 2 shots (Zygarde, Umbreon, Volcanion, Espeon, Ninetales, Lapras and others that hit for 110-200 are weak to Gardevoirs bulk, and either Whimsicott's or Aromatisse's utility)
Decks that attempt to wall (Jolteon, Glaceon, Carbink and other similar walls do not fair well as you have damage from all types of sources. Always keep in mind Whimsicott's attack moves damage counter so it's not stopped by Glaceon's Crystal Ray effect.)
Tauros (Xerneas walls so hard especially with Pokemon Center Lady)
Unfavorable Matchups:
Damage Spread and Snipe (Trevenant Break, Decideuye sniping Whimsicotts) though it is a slightly favorable matchup against Ninetales
Sylveon (sometimes you just get lucky though, totally winable)
Lycanroc (having only played against the Raichu one once that matchup isn't bad, but duo Lycanroc is a problem for Gardevoir usually)
Primal Groudon (focus sash too good, but just refrain from playing a stadium)
Greninja (as it only gives up 1 prize and can take out a M Gardevoir in 1 turn, less unfavorable in expanded though)
And most importantly decks that just setup faster. Whatever they are if they can pump out damage it's not too easy and not too hard to fall behind with this deck. Things that 1 shot your Xerneas can be a problem as it's 130 HP is so heavily relied upon. Not currently a problem as 130 and 150 are very hard to hit in current meta.
Questions or playstyles on any matchups I can help there too. Keep in mind only Whimsicott is rotating in September. Good Luck!
