The guthix mjolnir is a two-handed members-only weapon. There are no level requirements to wield it. To obtain one, either complete the Enchanted Key miniquest or trade with another player.
As its name implies, the guthix mjolnir is affiliated with the god Guthix. It is tipped with a symbol associated with Guthix, the Tear of Guthix.
Each mjolnir can only be obtained once per account, as the enchanted key will disintegrate after the player finds all of the treasure. Once this happens, the key cannot be re-obtained.