Odin is limited to the Black Shroud. Behemoth is random, unknown to be connected to any area. It is rumored that they will spawn only one time per week after reset. Odin will always be accompanied by a fog or a haze in the Black Shroud areas. However due to the capacity of servers Odin may be the hardest to kill since he spawns in relatively low areas so people will be there in great numbers to watch.