We apologize for the fact that you could not find the Ghost Napin monster. Because it is a private server with high EXP and easy retrieval of items, the MEGAMU administrative team found it unnecessary to set up and configure NPC quests, so some of them may be glitched in a way that they can never be completed.
In any case, the information provided by Setokaiba is correct. Ghost Napin's default spawn is at Peace Swamp (Swamp of Calmness). If you can not find it there, we advise you to give up the mission.