Reality is what you make of it and how you percieve it. At least in general terms. Perhaps by not making a plan or acting in an organized fashion, we might be able to catch this creature. After all, he expects us to be orderly, he expects us to act in a recognizable fashion. So we must not be predictable. the demon sighed, frustrated. Do not feel alone my friend. I'm out of my depth here as well. But as you say, if we do not act quickly, we will loose this chance. About the only thing we can do once we capture this creature is ask the gods for help in keeping him under wraps. We can't do it by ourselves.
"How do we catch someone who doesn't exist? By definition, he does exist somewhere, just maybe not in our reality. He can change reality, but not every reality. He has cheated death, so he might be an enemy of death and the natural cycles of the world. The gods Kelemvor or Osiris might be able to help us, perhaps we can approach their clergy." she held out her hands in supplication and frustration. "I can pray to my goddess for help and tell her what has happened, that Shar is involved. We should all pray to our deities for that matter. It could not hurt and can only help."