Without Life Orb there's no point in using Last Resort. Pixilate's great, but not enough. Good point about using multiple attack moves, though -- that way, I can't be ruined with Taunt.
Ground is super effective against both Poison and Steel, but Sylveon only has access to Dig. Or HP Ground, of course, but that's Special and this is a Physical set. Of course, Wish/Dig isn't a bad combo. No Fire or Fighting moves, and only Synchronoise for Psychic, so looks like Dig is it. Maybe Curse/Wish/Dig/LastResort.
You know that Sylveon is rocking a 65 Base Power Attack. Last Resort is really going to do nothing. Sylveon's SpA, HP and SpD makes it a much better Special Wall than even trying to use Last Resort despite it being 140 Power and 273 Power after Pixilate and STAB.