Mystic mud staves are the same as regular Mud battlestaves, but with greater bonuses. You can obtain this staff from Dagannoth kings, or take a Mud battlestaff to Thormac at his tower south of Seers' Village, who will make it to a Mystic mud battlestaff for a 40,000gp fee. Mystic mud staff requires level 40 Attack and 40 Magic to wield.