The Silvermoon Magisters are a pair of elite level 70 blood elves that can be found on the Horde side of Stair of Destiny in Hellfire Peninsula.
These two women have created a portal to Orgrimmar where reinforcements arrive to aid in the battle against the Burning Legion. Orgrimmar Grunts, Orgrimmar Shamans, Darkspear Axe Throwers and Undercity Mages, and from time to time, Melgromm Highmountain, all come out of the portal and rush to the base of the stairway to aid in the battle against the Burning Legion forces led by the Pit Commander. Without these Silvermoon Magisters, there would be no reinforcements to help the Horde forces and so they would be in danger of being defeated and driven through the Dark Portal back to Azeroth.