What Format?
If I assume OU, Sylveon is outclassed by Chansey as a Wisher, and Hyper Voice is way better than Swift anyways. :P
Don't use Amnesia, or any move that boosts a defensive stat and nothing else, unless you are using Sigilyph, or you won't need to switch as well as Phazing/Hazing being uncommon/Non-Existent. :P
That being said, you Should probably replace Amnesia with Hidden Power [Fire] or Sludge Bomb; HP Fire Gives you Steel and Grass coverage that Grass can't do much to, while Sludge Bomb gives you stronger Grass coverage and Damage while missing out on Steel coverage. :P
