I shot an evoker with a bow at a distance far enough for it not to see me. First arrow made it begin the animation to summon vexes, but I shot it right when the summons occurred... Now there is a permanent looping spawn of vexes and fangs stemming from that location. I tried to get a screenshot, but there are at least a couple dozen vexes targeting me, so all I got were a few waves of fangs coming towards me.

I saved a copy of my world just inside my nether portal (which exits onto the mansion's roof where the activity is), but the compressed folder is still 1.4 GB so obviously I can't post that here.