Picture this. You're fighting a Malamar with the ability Contrary (reverses all stat shanges on that Pokémon) that used Superpower to raise its Attack and Defense 3 times. You then use Topsy-Turvy on the opponent. Keeping Contrary's description in mind, what would happen?
Remember when you could rematch N in Black/White 2 and his team was different depending on the seasons? Why not have a seasonal tournament. E.g. Winter would be Ice and Water types while Summer would be Fire and Grass types.