Librarian Skeleton added?

Marking a spoiler just in case.

I was just in the dungeon and died (lol). But right as I did, there was a "librarian skeleton" enemy on screen. It had brown robes and formed a glowing sigil behind it. I've only done two or three full playthroughs before, but I've never seen it before. Neither the new patch notes nor the Terraria wiki has anything on it. Was it just stealth added to the new patch, or was another creature renamed? Kicking myself that I didn't get a screencap. Looked a bit like the Ragged Caster, but mousing over it definitely said "Librarian Skeleton".