Okay, you enter the boss room only to be confronted by hordes of Darknuts as a boss. (or some other enemy that comes in numbers more than 1) Simply kill one of those darknuts, press F6 and continue. Fight your way back to the boss room, voila, you kill one enemy, continue and the rest are dead too, leaving you a HC. My, that took the fun out of things didn't it? And the darknut room was marked: Dungeon Boss. Might want to fix that flag to account for ALL enemies on the screen and not just a single one.