Sylveon @ Pixie Plate / Life Orb / Leftovers
Ability: Pixilate  
EVs: 252 HP / 40 Def / 216 SpA  
Modest Nature  
IVs: 0 Atk  
- Hyper Voice  
- Moonblast 
- Shadow Ball / Substitute
- Protect

252+ Atk Muk-Alola Poison Jab vs. 252 HP / 40 Def Sylveon: 332-392 (84.2 - 99.4%) -- guaranteed 2HKO
rest in spa to hit hard

Sylveon @ Choice Specs
Ability: Pixilate  
EVs: 252 HP / 40 Def / 216 SpA  
Modest Nature  
IVs: 0 Atk  
- Hyper Voice  
- Shadow Ball
- Psyshock
- Hyper Beam / Moonblast