I have never seen admin mentioning anywhere that he added new Invisible monsters so i bet this must be a bug o.o
Sometimes on map you can encounter “glitched” tiles. When you walk on them, you get moved back away one tile. I thought it was simply a map bug and ignored it by walking around. That was until last night incident happened….
I tried attacking glitched tile (don’t ask me why). It took damage and after few hits it gave me myst. So i assume it was some random invisible monster with ~100 – ~150 hp. It gave 13 or 16 myst. After i got myst (killed it), i was able to walk on tile again.