Roar and WW don't just screw up who gets healed by Wish, they directly cut down Sylveon's recovery, as they bypass Protect. This makes Skarmory and Heatran two of the biggest threats to Sylveon, as they can easily switch into her and prevent her from healing. The best one can do is have trappers, such as Magnezone and Dugtrio, to take care of those two. Or you could pack very dangerous Pokemon that can use those two as set-up bait, to discourage them from switching in, such as Tail Glow Manaphy and Fire Blast SD Garchomp. Specially defensive Hippowdon also doesn't mind Hyper Voice and can phaze Sylveon at will, so it's another one of the best counters to Sylveon. Definitely mention those in checks and counters, and in the team options section, where you will suggest Pokemon to take care of them.
For the reason stated above (Heatran and Skarmory, two extremely common pokes, making Sylveon their bitch) i think that RestTalk Sylveon with Heal Bell + Moonblast should get at least a set details mention, if not main slashes on the set. Many teams rely on Sylveon to deal with many very threatening offensive Pokemon, such as Kyu-B, Dragonite, Lati@s, Conkeldurr, etc., and being unable to do this if the opponent has Heatran or Skarmory sucks and is way too unreliable. Missing out on Wish passing sucks, but RestTalk + Heal Bell is an extremely potent and reliable combination, not to mention that not all teams want Wish support.
