as i know the server/world changer is only appears once in awhile, the reason of this happens cuz of overlimit number of players inhabiting in one server, in order to stabilize the server, SE creates a new server and an NPC called world/server changer, then migrate who ever wants to move to other server that less laggy, or other reasons could be address for world migrating.
if this info feed you well, im glad, if its not thats all i know xD