What you gotta do is put it in on something that is not a wall. There, the Choice Scarf won't matter.
To counter it, besides Zorark, get something that would stink without it's Ability. Like Azumarill or Medicham. Without their Pure/Huge Power, they're useless. And Ditto will be useless (almost), because it's using Impostor.
If you're using it, switch into something that would be awesome without it's ability, like Regigigas, Slaking or Archeops. There, Ditto would be great.
Unless I'm so wrong and it actually does keep the opponent's ability. ._.
Then...oops. Hehheheh
Well, I think you all got this Ditto covered, but there's always the choice of another Choice item, unless you switch into something like Chandelure with a Choice Band equipped. So that's kinda situational, but could work out because most teams don't just want only a special attacker, because Chansey exists. And they don't want only physical, because Burns/Confusion would ruin everything. Or maybe a Ferrothorn with a Rocky Helmet. Or a Forretress.
Hmm. I'm thinking MASQUERAIN next. Cause it's awesome.
Or...Gastrodon or Genesect. Yeah. A Bug/Steel. I mean, there are as many as pure bugs, right?
Accelgor, Volbeat, Illumuse, Pinsir, I've been thinking too long. KRICKITUNE. TailGlow Volbeat=eh, Pinsir=eh, Accelgor=ehhh, Illumuse has no value to me.
Then there's Escaviler (who I vote for), Genesect (voting!), Forretress (vote), Durant (I'm voting for this one), and Scizor (Wow this is annoying to counter...along with Breloom...who I vote for)