The Man on the mountain pass

I assume by now many of you had faced him and had many fun times pushing him in to the ravine, however every time we face him he only becomes more powerful. Now he has the ability to misty walk seemingly indefinitely and is gathering apprentices. hopefully we can gather a team strong enough to finish him before we eventually have to find another way through the mountain. Quick note he also now has a personal vendeta against Azazel for killing one of his apprentices and likely Orma if he see's Orma in the fallen ones armor and wielding his blade 

Orma recently identified the race of the man as a Gith, an inhabitant of the ethereal plane. He appears to be training younger giths as they must step into the material plane to age and train. They have glowing silver greatswords and all of them can misty step, even the recruits.

One must ask, then, how are they traveling to the material plane? Is there perhaps an entrance or portal to the ethereal plane nearby? If so, closing it must be the top priority here. 

Excellent idea