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I suppose you were using the EV set that Smogon recommended for you. You did notice that on Smogon their move-sets had attacks right?
252 hp / 252 speed / 6 whatever sounds good.
I guess that is a good move-set if your just going to Sub - > Toxic - > Dance -> Pass.
Are you using Toxic hoping...
I'm not sure if the effects will stay forever if you just leave it in the box.
You would get quadruple the amount of EV if you have Pokerus and Macho Brace.
My Pokerus lasted about three days, I hear it varies though.