Sorry, I don't mean literally invisible but more like blending in with the crowd "invisible". Back in I think 05-08, when it seemed like every other month, some Korean f2p would come out, I remember there was like at least 2 I played where the blacklist made use of "grey robe" tech, which was that thing visually killed any outfit and replaced it with feneric outfit on your screen (but you could also set it to display in server too). Anywho, I remembered that if you blacklisted someone, the next time you restarted your game and loaded back in, you would look like a "grey robe" player to that person and they'd have to be super close to that person to see your nameplate (but usually, some took the extra step to name change) thus blending you in with the crowd. So I just personally called it invisible mode.