Virtual Muggings in Lineage II
In FFXI, GMs can take the form of standard PCs, albeit wearing custom armor with cool fiery effects and massive amounts of defense. They can sit in an area, invisible, if a player calls them to watch TOS violations taking place. They can teleport players to jail, which is an area called Mordion Gaol. They can also free players who have accidentally become stuck in the landscape. The only difference is that they don't walk a beat; they only appear when called. My understanding is that they have enough to deal with that they don't have time to simply walk around, and of course, raising player fees to provide more GMs probably wouldn't go down too well.