The Sunless Cell/Walkthrough

Your fireteam spawns in the Mausoleum, right where you begin the Shield Brothers Strike. You proceed left over into the Founts through the hallway, where some Acolytes and Thrall will spawn, along with a couple Wizards. Once you kill the last Wizards at the back of the room, the doorway next to it will open, leading you to the next room, where you will have to disable two batteries in order to proceed.

Each battery is located across an abyss with two rotating platforms to jump on. Once you near the batteries and kill the two Wizards, summon your ghost to disable them. A Shreiker will spawn and you must kill it. Jump back over to the main platform and kill the enemies that have spawned. Once both batteries have been disabled, you my proceed, where you encounter several waves of enemies. Clearing each wave summons the next, with four waves total. After clearing this section, an Ogre will spawn just outside the door. Kill him, and go to the next room, where there are several Shriekers and many enemies. There are two doors at the far end of the room, only one of which is open. Once you've identified which one is open, clear enemies as needed, then run to the exit. Once through, there will be a long bridge you'll have to cross. Several Thrall will run at you, and you can either run past them or kill them.

There will sometimes be a crate containing either special or heavy weapon ammo, and your team will jump down into the cell. There is a small circle in the middle of the room with faint light emanating from it, with no other sources of light in the room. Alak-Hul will spawn once all three members of your team are in the cell, and you must then kill him. Alak-Hul is equipped with a large ax and will charge at whoever he focuses on. His attack will deal the most damage if he hits one of your teammates, but also if you are standing near him. There will also be a variety of Thrall, Acolytes and exploding Thrall that will attack you. Once you defeat the Darkblade, he will drop two or three engrams and sometimes a consumable. A Strike Hoard will also appear in the middle of the room, open to anyone who may have a Skeleton Key.