Gravewalkers, The Ritual and Reversal of Fortune are two missions as part of the Eltariel storyline in Middle-earth: Shadow of War.
If you are interested in completing other missions in the game, our Shadow of War guide and walkthrough can help.
Prerequisites: Complete Fire and Fury, cleanse all Haedir Towers in Gorgoroth.
Reward: 20905 XP, 1060 Mirian
Investigate Nazgūl Activity/Follow Eltariel.
Defeat the Wights: a fairly straightforward fight - these may be spectral humans, but they can be dealt with the same way as Orcs.
Defeat the Wights: more Wights are patrolling the walls - Eltariel will run off and take a few out, so head in the opposite direction to her to cover ground more quickly.
Follow Eltariel. Defeat Isildur: As with all the Nazgūl fights before, the usual strategy of dodging his attacks, using Stun when prompted, and getting in behind him for a few extra attacks should see him off fairly quickly.
Eltariel will eventually deploy her Light of Galadriel, and when she tells you to get inside her shield don't argue, just run for it - Isildur will close in for a volley of attacks, and then leave.
Defeat the Wights.
Prerequisites: Complete Tower of Sorcery, cleanse all the Haedir Towers and capture the fortress in Cirith Ungol.
Reward: 10625 XP, 960 Mirian
Bonus objective: Stealth Dominate three Archers.
Bonus reward: Wealth gem.
Disrupt the Ritual: Climb up onto the walls and use Stealth Dominate to disable the archers as you head towards the marker - this both makes the ensuing fight easier, and fulfils the optional objective.
Defeat the Nazgūl / Defeat the Orcs at the Ritual: The Nazgūl can be dealt with in the same way as all the others - dodge attacks, Stun when prompted - but we'd suggest opening by Dominating one or two of the Captains rather than killing them; the Nazgūl doesn't seem to attack them and will stay focused on you, so you can kite him around while the Captains do him some damage.
Need more help? Our Shadow of War guide and walkthrough gives you an overview of everything you need, but if you need something in particular, we have pages on Shadow of War Fortress Sieges, how to earn Mirian in Shadow of War, a guide for how to import your Nemesis and Follower to Shadow of War, collectibles guides like how to get all Shadow of War Legendary Armour and Weapons sets, a list of Lost Artifacts and Web of Fate locations, and Ithildin Door poem solutions and Shadows of the Past, along with how to grind XP in Shadow of War to power through the tricky Shadow Wars endgame and get the true ending. Finally, there's Shadow of War's army building explained and the best skills and how to earn Skill Points.
Reversal of Fortune
Prerequisites: Complete all previous Eltariel quests.
Reward: Shadow Dominate skill upgrade, 11370 XP, 970 Mirian
Reach Eltariel / Disrupt the Ritual: Head to the marker.
Defeat the Nazgūl / Defeat the Captains: The Nazgūl can be dealt with in the same way as all the others - dodge attacks, Stun when prompted - but we'd suggest opening by Dominating one or two of the Captains rather than killing them; the Nazgūl doesn't seem to attack them and will stay focused on you, so you can kite him around while the Captains do him some damage.
Rescue your Followers.