The Idea: Flesh eating shadows don't just kill your friends in a matter of seconds, they reanimate their corpses for their own gain. The scary thing about the Vashta Nerada, piranhas of the air that disguise themselves as shadows, is that they're here on Earth. In small swarms, admittedly, but they live off roadkill. The truly terrifying thing about them is that they reanimate the corpses of the people they've just devoured. Not satisfied with stripping people to the bone, they then form a body and attack everyone else using the spacesuit of their victim; imagine you're one of that team that lands in the Library. You don't just see one of your friends brutally murdered, you see their skeleton reused by their murderer, just so that they can come and do the same to you. If that happened to one of you friends, you'd be scarred for life, without a shadow of a doubt (and I'm not sorry for that pun). Even the great River Song, killer of Daleks, survivor of Weeping Angels and wife of the Doctor, couldn't defeat the Vashta Nerada. It's not video games at all; the reason libraries aren't as popular as they used to be is because of flesh-eating shadows.
