Revealing mistake: Mulder and Scully find Katlyn in a freezer/fridge hiding, and Scully says that she's hypothermic and they need to get her out of there. As soon as the cut scene ends, both Scully and Katlyn turn to face Mulder, and their character models clip inside each other.
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.
