Note: The caragor riding skill is extremely useful here, if you haven't got it already.
This mission returns you to Minas Ithil, after your layover in Cirith Ungol. The cutscene will see you delivered into the enemy camp, to face their champion. Well, champions, really, though you'll start with some one-on-one combat, most likely with an Olog.
The best tactic here is to free one of the many caged caragors around the arena's outer edge. You can ride them for damage and, if you're lucky, the orcs will do the work of breaking them in for you.
When this first champion is downed, go to the center of the arena and taunt the crowd (watch your back for any stray caragors you may have let loose). This triggers a fight with a mob of no-name orcs, and two captains. The caged caragors continue to be your best weapons, both as mounts and roving death machines.
When the two captains are down, a final Nemesis champion will take the field. He'll be the toughest of the lot, but between the caragors, the ample space for kiting, and jumpable walls, he shouldn't be a problem for long.
This death triggers the final, rather glorious-yet-terrifying cutscene, and mission completion.