Alright everyone. My question is how a DM should handle a changeling? I have a player in my game who is under the impression that he can commit any crime and simply change his looks and bluff his way out of it. Now, that's fine... I don't have a problem with him "THINKING" that he is going to be able to get away with every crime. As a DM what might some counters that I can through his way to keep him in check?
Well, unless he's the only changeling the world has ever known, the agents of the law will at least
consider the possibility that one might be involved. (And even if he's the only changeling ever, he's almost certainly not the only rogue ever to have tried a magical disguise!)
As I see it, there are two possibilities: when he uses his changeling ability, he either disguises himself as "real people", or he disguises himself as someone who doesn't actually exist.
If he uses a "real" disguise, it's likely that the investigators will initially hunt down said "real" person. At this point, they'll (eventually) realise their mistake and then both they, and the other victim, will be after the changeling. (Of course, they won't know
which changeling, but...)
If he uses a succession of "fake" disguises, the investigators will get to "it's a changeling" rather faster... but at least then he won't have made an enemy (as above).
Either way, the investigators will likely proceed by hunting for the things that the changeling stole, rather than the changeling himself. So, they'll have agents combing the black market, will trace back through the fence, and eventually get to the rogue. Or they'll use locate object, or...
(If you
really want to know the best way for them to proceed, have the PCs get robbed by a changeling rogue, and see how
they proceed. Whatever they do, adopt as SOP for the local law enforcement!)
The other thing law-enforcement are likely to do, of course, is start to set traps. Either to detain the changeling immediately, or to mark him in some way so that he can't simply change form and get away, or similar. Oh, and wealthy property owners will do the same, too!
(And all that's assuming that the powers-that-be haven't dealt with the problem at the source. In a "points of light" setting, it's quite likely that changelings need to either be registered or be working for The Man, or else be at risk of summary execution when found. Remember - due process and civil rights are features of
our world; there's no guarantee that they'd apply in any other world.)