Dryads, and I didn't even hunt them down specifically. They just get spawning in those annoying woods, and I'm not the sort of person to flee from a trivial encounter! So I just kept killing them all.

It actually gave me a jump when I saw the Last One though. It was night in the woods, and just in the distance I saw this aggressively pink creature coming towards me and I was like "what was that!?".