Guardian of Blizzard

Guardians of Blizzard are World of Warcraft mobs that Blizzard Entertainment created to ward off curious players from entering unfinished zones during alpha and beta testing stage of the game. They usually appeared as infernals (but could be any number of different creatures, including rats); however, they are much more powerful. They posess a spell called Death's Touch which one-hits any player.

This function also existed on mobs in any completely-closed, yet populated, zone during the earlier testing phases, since there were ways of easily getting past the Guardians.

Disappearance
Since the release of World of Warcraft, Guardian of Blizzard has virtually disappeared from the face of Azeroth. The mob can still be spawned by Game Masters as seen in the video below. The guarding function of preventing exploring players is replaced by the No Man's Land effect on test servers.