I was playing in a new hardmode world a while ago. (I mean that I made a new world, then set it to hardmode with TEdit. NOT the one in that challenge run.) When suddenly, some new monsters appeared. There was some kind of new replacement for the Wraith, I think it was called the Reaper, that appeared out of nowhere. When I killed it, the sky suddenly took on a subtle orange color, and more monsters showed up. I remember what looked like some kind of variant on the Devil`s Eye, but I didnt really get a good look at it because it was blocked off by a wall. Anyone know what this is about?

EDIT: I forgot to mention this before, but no, there was no system message.