I dunno if you need another world file for the anachronism thing, but I finally ran into an indoor one that went funky. It didn't spawn ANY native monsters whatsoever; in the save, I have explored the big room, and there are 4 anachronistic monsters left, and they're the only ones in the room. So here's the file if it helps, character standing in that room. This is a new world, too.
....and yes, I named the world "Batman", I couldnt think up a good name, first thing that came to mind.