Remember those Devilsaurs in Un'Goro crater? Remember how they were giant, and ten levels above you at the time, and how they'd sneak up behind you somehow and eat you while you were peacefully picking a herb? Well, meet the Fel Reaver.
Fel Reavers are giant, level 70 plus automatons that roam the Hellfire Peninsula - BC's starting area. Much like the Devilsaurs, they are extremely large, deadly elites. However, they do make the ground shake long before they get to you, warning you to run far, far away. I didn't feel like testing out how hard they hit, but other testers reported 2300 crushing blows on cloth.
Because of the size and shaking of Fel Reavers, savvy beta testers learned to quickly avoid the enemies. And so Blizzard, in a pretty hilarious display of evil, replaced the skins of the Fel Reavers with those of bears. This added a new level of terror, as confused players looked around for the Fel Reaver after seeing the shaking, failed to notice the bear, and got pretty much insta-owned. This led to a lot of confusion and a lot of bad puns. The Fel Reavers are back to normal now, but the Fel Bears made quite an impact on the Beta community. When someone suggested that beta testers should get a special non-combat pet when BC goes live, one of the options was that of a bear cub with "Fel Reaver" written over its head.