Here's something I've learned @ shary&shaui by not running full team suggested here:
1) Chansey/Blissey easily walls thundurus, focus blast does only roughly 33% to 252HP/252Def chansey with eviolite, you dont need to sac forretress here
2) If you send Skarmory into Cobalion he will spam Close Combat and you can easily outsustain it with Roost, once he's -6/-6 you can oneshot him with mach punch from conkledurr (but some fodder has to die first so conkledurr doesnt get hit), alternatively you can run some damaging move on skarmory to take it on (brave bird?) since toxic doesnt work
