Character mistake: In the pause menu/inventory screen, Mulder's "Department of Investigation" ID is visible, complete with his photograph and a few other details. However, the crest and logo and the big letters that say FBI are missing from what is shown on his ID from the show.
Plot hole: After Mulder is bitten by the zombie, Scully works on making an antidote while Mulder fights off more zombies coming. Somehow, she does an autopsy on the zombie doctor, analyses the blood and toxin, and rapidly comes up with and makes 3 doses of an antidote in a mere few minutes' time. Yes, it's a video game, but that's unbelievable even for the TF2 Medic to accomplish.