UPDATE 24/07/2014 8pm: GameStop has confirmed to Eurogamer that while the Red Hood DLC is currently a GameStop-exclusive, it will be available post launch in the marketplace.
ORIGINAL STORY: 24/07/2014 3.45am: Batman: Arkham Knight will have story-based DLC based around Red Hood that's exclusive to GameStop.
We've contacted GameStop to see if players who miss out on the Red Hood Story Pack will be able to purchase it later. We're currently awaiting reply, but will update as we find out more.
Additionally, GameStop pre-orders come with the Harley Quinn Story Pack, but this is true of pre-orders elsewhere and isn't exclusive to the chain.
GameStop has been making an effort to attain exclusive gameplay DLC, which has worried a lot of gamers concerned with artistic integrity. Nevertheless, GameStop said of its initiative to help fund games in exchange for exclusive DLC, "We will not be involved in the creative process - the artistic design and development - that's not our domain!"
Red Hood is a mysterious villain that's been reinvented multiple times throughout Batman's lore. He began as the Joker's identity back when he was a petty criminal before he fell into a vat of acid and came out looking like a killer clown (a look he really grew into, wouldn't you know). Red Hood is most prominently featured in the fantastic animated film Batman: Under the Red Hood, where he's a crime-fighting vigilante who isn't afraid to kill Gotham's most despicable criminals.