What is it about zombies taking down helicopters? Kill 500 zombies between you and Union City to unlock the Blood Vial card.
The Slaughterhouse 500 Challenge was a challenge for the game The Last Stand 2 that was released on July 17th, 2008 and lasted until July 24th, 2008. To complete it, the player had to kill 500 zombies. Completing the challenge would give the player the Replay 1 version of the Blood Vial card.
Contrary to popular belief, this challenge was not named after the novel Slaughterhouse-Five. Rather, it was named fairly arbitrarily, as a very obscured reference to the movie 300 and the notion of a slaughterhouse.