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Oh that's a tricky one. It does hit a lot of the metagame hard but unlike Thundurus-T it doesn't get nasty plot to break down walls and it's typing doesn't offer as much resistances that really makes Thundurus-T shine... Maybe A or A-?
I'm confused!
Personally I never thought Landorus was that great from using it. This was mainly because of it's speed. I'm still a newbie to this thing and not entirely sure how a suspect test works out. But the general idea I'm getting from reading this is that Landorus is amazing on it's own...