Another problem is why that oil painting monster, which has at least a half-step Epic level, appears in this mission. Given Feather Song's current strength, the difficulty of the mission [Blood Grudge Filling the Window] had long changed from 'Extremely Dangerous' three months ago to 'High', even lower than when she initially did [Nightingale's Farewell]. Under this condition, the appearance of such a powerful monster in this haunted house seems somewhat unreasonable.
The answer is simple. The monster, whose power somewhat breaks the norm, is actually not an enemy of the uninvited guests Feather Song and Motan. Of course, there's a possibility it could turn into an enemy and achieve a double kill, but it's just a possibility. In fact, unless certain thresholds are hit, the monster hidden in the oil painting will generally remain neutral. With enough convincing, those on the quest could even persuade it to become an ally, greatly reducing the mission's difficulty.
