Genius-level monsters (and other opponents) have always been a problem for me. Talysman at The Nine and Thirty Kingdoms suggests a mechanism for handling it. The original post “I Meant to Do That” was originally posted almost a year ago (sigh I still mean to go back and read this site in more detail) and suggests periodically allowing an Intelligence-modified check for ‘clever planning’ if the opponent is smarter than the PCs. The GM might not be able to correctly anticipate what PCs are going to do, but the genius they are acting against has.
I’m conflicted here. Part of me figures that once the scene is set the GM should not arbitrarily change things around… but on the other hand, this isn’t quite arbitrary, is it? Having just the right thing, or at least a pretty good thing, in place when needed is a sign of intelligent planning. I’m probably not a genius, but I’ve found a number of times that things I’d done ‘because they are a good idea’ truly end up being so (I like surprising myself that way. “It would be really handy if… huh, I did set it up that way, cool.”)
He expands on the idea in discussing GM-Ordained Betrayal,where possessed or doppelganger-replaced characters don’t necessarily have to have the player explicitly act against the party… but instead ‘things that happen were caused by the affected character’. There are some questions about how to discover and resolve the problem and some potential answers. Possession isn’t particularly a problem because the target needs to be alive to be of any use, but doppelgangers may be problematic because by the book they kill their targets.
So far, I like the idea that instead doppelgangers can only impersonate someone who still lives. One suggestion was that while the doppleganger impersonates someone the target is in suspended animation (and thus does not starve). Honestly, though, I prefer that the target is left otherwise in normal shape. He might be unconscious or tied up (and hidden, if the doppelganger is smart) but the doppelganger is limited in how long his impersonation lasts… unless the target is maintained. The king the doppelganger impersonates needs to be kept alive, and possibly close (for some definition of close) to the doppelganger for the impersonation to continue to work.
Something I’ll need to think about. I’ve often avoided such opponents because they were a pain (one way or another), but the mechanisms here look like they could resolve it.