Gotham City Impostors is due to arrive on Xbox Live Arcade tomorrow, but the downloadable content is already online for you to browse. Shockingly, there are over one hundred items to peruse and buy, all of them being superficial character customization pieces.
The prices range from 80 to 320 Microsoft Points, although according to Monolith, the costume pieces are unlockable for free in the game itself. So, you're actually paying the game extra money for the chance to play less of it, which ... doesn't seem like a sound purchasing decision.
In any case, you can go online and look at Batz Pants or Jokerz Shirts if you want.