There are a few bosses in Azeroth that can Frenzy. While frenzied their size, attack speed, and damage increase dramatically. However it can be removed by a Hunter using Tranquilizing Shot. Mobs that frenzy include Chromaggus, Magmadar, Flamegor, Maws, Princess Huhuran and Hakkar the Soulflayer when High Priest Thekal isn't killed.