Enormos is the large Mammoth mount of Vladof the Butcher. You encounter Vladof as the 6th and final boss in a "Ring of Blood"-like event which takes place in Zul'Drak, Northrend. You must defeat him (temporarily), which knocks him off Enormos. Your party's tank can then mount Enormos, and make use of the Mammoth's abilities to tank, damage, and finally defeat Vladof.