Dark Rune Thunderer

This mob will put a nature damage increase debuff on your tank, after about 10 or so stacks your tank can get one shotted. Swapping tanks works, the paired mob in the pulls puts a reduced armor debuff on the tank.

Ability

 * Lightning Brand-Shocks the target for 2500 (3500 on Heroic) Nature damage to the target, and increases Nature damage taken by 40% for 20 sec.