Placeholder mechanics

[aaronp]

So could someone give me details on how "placeholders" work?

Do you always need to kill a placeholder for a mob to spawn? For example, the other day I ran into this guy in the aqueducts. Dude attacked me for no reason (I woulda given him some change if he asked) so I had to hack his face off. I haven't seen him since (I was hoping to find a higher resolution image for the wiki), there's always a rat that spawns in his place.

Another example is the orc runner in bb. I killed him by chance once, and found that he has a pretty profitable quest at that level, so I went about trying to do it again, only to find a green Centurion where he spawns. I killed that thing probably 10 times or more before giving up. Would I need to keep killing the Centurion for the runner to even show up?

Sometimes it's obvious. For example, in the thug and smuggler camps in the aqueducts, sometimes there is a chance that a leader will spawn instead of the usual mob.