Well, I don't really like CM lugia. It's really supposed to be a wall. But in this case it would have to be Shadow ball. The reason being is that punishment increases in power the more boosts your opponent has not you. So you'll be getting no boost from it. Shadow balll also just is baws in general :D
But seriously use a walling set.
Lugia @ Leftovers
EVs: 252 Def / 252 SDef / 4 HP
This capitalizes on Lugias epic 106 / 130 / 154 defenses. It can take virtually any attack at full health. it then can set up any sub and blow the opponent away with whirlwind or toxic them for greater damage.
Hope I helped.