Okay, I have looked everywhere, and someone told me it was in Chaosrealm in a hut at D7 at 4AM. Well I found the only hut in D7 and I went in there every second from 4AM to 5AM, and I did it for a whole month, and nothing. Does anyone truely know where the key is to coffin MO? I believe it unlocks the Dragon King's Arena.