Took a look at the Nexon "careers" page

You might want to be careful calling them out when they are in invisible mode. For them, a player knowing that they are there when they are invisible is considered proof that you are a hacker and grounds for banning. I know you are sensing their presence from lag or loss of aggro , but they might be poorly trained or just looking for any excuse to fill their quota of bans.

Oh I'm not too worried about that, figured the game isn't worth playing anyway if I end up getting false banned. But thanks for the suggestion.

Most of the time there's no lag or aggro change from an invisible GM being present. I do see a lot of mobs in Scrubby Garden on my runs though. Mobs do not spawn there unless somebody gets warped there, and mobs on any map do not move when there's nobody on the map.