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Mercury elementals are a new type of elemental comprised of pure mercury, they were first introduced in World of Warcraft: Cataclysm. It's unknown if this is a naturally occurring elemental or something that requires a ritual to become. In Deepholm a Twilight's Hammer member performs a ritual by feeding on Mercurial Oozes in order to "ascend" to another form. This process would transfigure his body into one of pure quicksilver. There are two types of mercury elementals, those that form an ooze and those that take an unbound water elemental form.