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Wizard Grayzag is a wizard on the 2nd floor[UK]3rd floor[US] of the Wizards' Tower placed outside the Lesser demon cage. He was once level 41 and attackable and would summon imps to assist him in combat. He can no longer be attacked and therefore no longer has a combat level. He seems to have a grudge against Wizard Mizgog, who stands across the hall from him. He is also in the story-line of the Imp Catcher quest, he was the one who told the imps to steal Wizard Mizgogs' beads.
When in conversation with Evil Dave, and asking him about his luck with 'demon-summoning', Dave reveals that he thought he should start small, asking Grayzag for help with summoning imps, but succeeded in summoning a level of demon even lower than that of imps - Hell-Rats.