Played a Greninja deck last night with my Sylveon deck. I'm sure my opponent was extremely disappointed when I used Lysandre and Plea-GX to put both of his evolved Greninjas back in his hand. I also beat it with Trevenant Garbodor.
Sorry guys, but Greninja isn't back. I wish it were, I loved playing Greninja and it won me a ton of matches back in December and January. Look for him again in September, but until FoGP rotates, the blue frog just isn't going to have the success he used to have. Plus, it's becoming more of the consensus that Volcanion may be played less because it's almost becoming an autoloss to Garbodor.
Trevenant Garbodor is literally its only autoloss and even that is closer than it should be. As for the Sylveon deck, I have consistently had the exact opposite happen and I am a terrible Greninja player. Basically, I very consistently N away everything Sylveon grabbed via Magical Ribbon over and over again. It probably helps that I am playing Red Card in my list as well leaving the Sylveon player as few options as possible as frequently as possible. Basically, I snipe the bench and use shadow stitching until I have cleared the bench of all Eevees (usually there are only 2 max on the bench any given game anyway, so this isn't some impossible task). The question comes down to resources and whether the Sylveon player can keep lucking into theirs while constantly being N'd.
In an interesting twist, you know how everyone expects Garbodor to change how decks are built? In my case, Sylveon has done more to change my approach than Garbodor. I have started adding more and more hand disruption cards to my decks just to make sure Sylveon has as bad a time as possible. I absolutely loathe that deck.