I considered my possibilities. Doctor Strange? No no, too obvious and a little overpowered, I grant you.
Reed Richards? He's as smart if not smarter than Egon and would have a pretty fair chance of figuring this out, especially since the Boogieman uses portals to enter and exit his dimension. But no... probably a little too overpowered. I considered robots incapable of fear, but Boogieman's powerset explanation says he can alter existing matter to suit his will. I take that to mean inorganic matter or else he could've just changed the Ghostbusters into termites and taken over the Earth.
All possible opponents I considered myself.
Guess I will have to go with... Angelus.
I don't know what an Angelus is. What is it with you guys and Buffy? I guess it's off to Wikipedia to educate myself. And away I go!