Follow the trail of this woken evil to fiery Gorgoroth, where an orcish necromancer is up to no good.
Your first task is to kill his acolytes.
Almost half are atop the tall towers here, so Shadow Strike is an ideal way to take them out.
The others are clustered around Zog- a flying stealth kill can you set you up to take most of them out at once.
Once the battle is joined, Zog will introduce himself, and then you'll want to kill everything. The conveniently placed grog barrels can be a help there.
Zog himself, however, will flit away before a death blow can be struck. There's nothing you can do about it- it's just the story.
Mop up any acolytes who may have somehow survived, then follow your marker down into the pit, where dark magics are worked, and Talion does his best Gandalf impression.
Carnan joins the fight, and the two deck it out kaiju-style. Your job is to shoot Tar Goroth in the back with charged shots when his spine lights up (usually after he's just finished pummeling Carnan).
There's plenty of elfshot in the cavern, so that's not a problem, but do be quick to avoid the falling debris, using sprints and dodges to clear the impact areas.
When you've sufficiently damaged ol' Tar and Feathers, he'll flee, and you'll want to jump on Carnan's back to continue the chase. As before, watch out for falling debris.
When you catch up with him again there's another round of fisticuffs. Keep up the pressure with regular pummeling, but your real opportunities for damage come from countering his attacks, so keep a sharp eye out for the cues, which allow for some devastating ripostes.
When he gets down to about 20% health, he'll grapple with Carnan, which flings you off her back, in perfection position to shoot his exposed heart area.
Let the charged shots fly, then chase after Tar one more time. Catching up this final time launches a cutscene in which things don't go great for Carnan, but the mission completes anyway.