Despite his earlier setbacks, Zog's cult is still going strong, this time raising the dead and attracting ghuls in Gorgoroth. Meet Carnan there- you'll be working with her Graug form again.
Your goal is to purify the three totems, with a secondary goal of destroying ghul mounds. This latter is pretty easy- you'll encounter far more than 15 mounds if you stick to the dirt paths here. Just stomp or pound them when you see them.
You can pound on the Revenants too, but Talion has to dismount to purify the totems, so work quickly, before the revenants wake back up.
Start with the rightmost one and work your way left. When you start to reach ranged resistance near the second totem, remember that Carnan has ranged attacks too.
At the same time, Carnan has a health meter like any other mount, so don't such recklessly throw her into danger- if she dies it's an automatic mission fail.
The third totem is in a minor cave complex. Use Carnan to soften up the area then dismount and take out the caragors on your own- they can leap on her back for significant damage. Shadow Strike dominations are a good way to pull their fangs, as it were.
With the caragors at your side, you should have enough elbow room to purify the last totem uninterrupted.
With this victory, Carnan flies off, and the mission completes.