I dont think it has time to setup both Sub and Nasty Plot. Try asking other QC members, I am leaving soon :[
Watchout for priority, Arceus's ExtremeSpeed which is very common will stop your sweep easily. Even Giratina-O's Shadow Sneak will pick you off in Salac Berry range and they are some users of Roar such as Giratina, Dialga or Arceus which foils your sweep. Focus Blast is really useful for Dialga and Ferrothorn. HP Ice is weak anyway and doesn't kill Latias. Rayquaza is 2HKOed by Thunderbolt.
