The fact that the zombies are all well known beloved characters instead of no name ponies and that the surviving ones have no choice but to gun them down or be devoured and torn apart by their former friends and family is what makes this more unsettling than any regular zombie pony fan art.

In short, the very essence of the zombie horror genre.

For some reason, despite all the video games I play, I find pictures like this far more disturbing than R34 content.