Rikudo Sennin (Shedinja)@ Focus sash
EVs: 252 HP 252 Sp defense 4 sp attack
Assuming that Evil Vap can't touch Shedinja with her filthy and unholy hands. It allows Shedinja to step into the godly level (+6) and slash this rascal with the sword of justice. Leaving an X mark of freedom and holyness on Vaporeon's belly. Not only that, it has Heal Block, the gimmick, stupid, and useless move. It stops Vaporeon from getting its forbidden wish. Leaving the wicked Mermaid cat unable to avoid her inevitable fate, the judgement of Shedinja.
Anyway ignore my bs, here is the boring calcs:
+6 252+ Atk Shedinja X-Scissor vs. 248 HP / 0 Def Vaporeon: 673-793 (145.35 - 171.27%) -- guaranteed OHKO