First : - a mon will always get walled by something, Skarmory ? Gliscor ? hell, they wall any physical pokemon, that's no surprise. Forcing the opposing team to pick hard walls like that who are easily countered themselves is a good thing. - Priority ? then Substitute forces them to take a hit, either on the switch or when they kill the Sub. There isn't many Mach Punch users that can take a CC or a SE so easily. Conkeldurr? Hitmontop ? x) However, Lefties are what ? 20% extra health in a whole game ? I rather have the possibility to kill frail scarf or stuff like that. What you seem to miss, is that when we put Cobalion onto Kyurem, the enemy WILL switch, and we will hit on the switch. After some play around, when Cobalions walls will be low enouhg in HP, the sweep can begin, not before. Hence the fact that Cobalion won't be spamming Substitute so much, and prefer a boost in Speed. I'm not saying Salac is the only possible item, but I don't see Leftovers doing a great job here, it's safe for sure, but I rather have some burst power.