The Tower of Sorcery and The Chosen are two missions as part of the Eltariel storyline in Middle-earth: Shadow of War.
These unlock one after another, and come after completing The Three Towers.
If you are interested in completing other missions in the game, our Shadow of War guide and walkthrough can help.
The Tower of Sorcery: How to beat Suladan
Follow Eltariel: This is a good opportunity to complete the optional objective and Dominate 15 Orcs as there are a lot of them stood around on their own - trying to do it during the upcoming boss fight is unwise.
Defeat Suladan: Start the fight by taking shelter in Eltariel's shield until Suladan stops attacking.
The remainder of the battle plays out similarly to your fight during The Fall, but you only have one Nazgúl to deal with but he's got a load of Orcs with him instead; these are something of a mixed blessing as they can be a bit of a hindrance but also make a handy source of healing if you're in trouble.
Suladan has a new attack and will occasionally fire projectiles at you, so dodge out of the green circles when he takes aim, and keep wearing away at him.
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.
Prerequisites: Complete Tower of Sorcery and cleanse all the Haedir Towers in Seregost.
Reward: 8675 XP, 930 Mirian
Bonus objective: Defeat more Orcs than Eltariel. (Must be completed before Reach the Captains.)
Bonus reward: 500 Mirian
Follow Eltariel, defeat the Orcs in the Camp.
Defeat Uruks as They Pass: In order to fulfil the optional objective and kill more than Eltariel we'd suggest heading up the slope towards them and eliminating them before they get close to her; she'll take a few down with her bow from range, but if they get within melee range of her she may take the lead.
Interrogate the Messenger: Make sure you don't accidentally kill the marked Orc, and instead Dominate him when he appears.
Reach the Captains.
Defeat the Captains: There are three to take on, and a Drake will show up to complicate matters.
If you have the skill unlocked we'd suggest summoning one of your own to even the score, and recruiting the Captains to fight by your side rather than killing them will make the fight go a little easier.