I remember when I was waiting for VT2 that I stumbled upon this video from IGN. After having gone back to memories and seeing discussions regarding what features was left delayed or not (such as dedicated servers and challenges.) I recall something very interesting that I saw that I haven’t seen anyone mention or see before ingame ever.
My guess were that this is exclusive to the Screaming Bell map after the bell activates (and the Skaven is supposed to go crazy/become stronger from it.) but since I play on very low settings and noticed no real performance changes to the skaven, I don’t think it’s ingame. I also thought it could be some kind of Heroic Deed mutator as well, but I’ve seen no deeds that modify enemies visually. Have you seen it?