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Why is switching scizor into blissey surprising? Scizor has superpower and u-turn and blissey can't do much to it if it's running toxic and doesn't have flamethrower.
Yeah, it would have been a good strategy if he had stuck to it, since a +6 gyarados behind a sub would have little trouble destroying the rest of that team. I actually think he should have gone for additional DDs to avoid wasting PP on his attacks
Not putting 252 Defense EVs on Blissey is crazy; doing so more than doubles its physical bulk and otherwise it will be destroyed by any physical attack.