What costume am I missing?

I have the PC version of Arkham Knight, preordered from Steam with the season pass and this missing gap is killing me and my OCD. I have already 200% the game, logged in with WBPlay, got 3 stars on all of the AR challenges, 100% the Harley Quinn DLC. But there's a blemish on my completion, the game shows I have 103/104 showcase items. The only things that are missing is this costume in the screenshot (9/14) and maybe 3 or so other achievements.

What is the missing costume in this version of the game and how do I get it?

As far as I know, I should have everything in this game at this point. Getting all achievements typically doesn't unlock game items so I wouldn't expect that to be holding me back.

Showcase

For reference, here's the names of the costumes in the slots (from top-left across):

  1. Batsuit V7.43
  2. Batsuit V8.03
  3. Batsuit V8.04
  4. New 52 Batman Skin
  5. Batman Flashpoint Skin
     
  6. Batman Beyond Skin
  7. Dark Knight Returns Batman Skin
  8. Anime Batman Skin
  9. missing
  10. Robin
     
  11. New 52 Robin Skin
  12. Catwoman
  13. Nightwing
  14. New 52 Nightwing Skin

It appears to be a Batman costume. And most listings I can find mix in console exclusive costumes so I can't be sure what belongs to what. No other DLC items have been released for PC yet and of course, we don't have any of the PS4 exclusives so it can't be the Adam West costume.


It turns out there are two costumes associated with signing up with WBPlay, one for getting an account and one for signing up to the WB Games forums.

The former grants the Anime Batman Skin. The latter grants the Zur En Arrh Batman Skin.

I only linked my account but didn't sign in to the forums. Doing so unlocks the reward.

Zur En Arrh