High Chief Winterfall has a guard in very close proximity. Before 2.3.0 he was an elite and had two guards; it was typically easier to crowd control the guards (sap, polymorph, etc) or offtank them and concentrate on the High Chief first, since he was the hardest hitter. After the Chief was down, the rest of the fight was easy, as his guards were normal Winterfall Furbolgs. Since 2.3.0 this strategy is obsolete though, as the High Chief is a normal mob and only has one guard.