Boethiah's Calling

Overview
"If in the reading, your blood boils in your veins, and your mind blazons with fire, then Boethiah calls you. It is then most wise to heed her call. Find her on the mount which overlooks Windhelm. Meet us there and be tested."

- Boethiah's Proving - by Anonymous

Walkthough
Note: VERY IMPORTANT. Quest only begins once you are a level 30, otherwise, the Sacellum of Boethiah will be empty, and you will never be able to find Boethiah's Proving. This quest can be initiated by finding the Sacellum of Boethiah. Alternatively, you may read Boethiah's Proving, which can be found at Septimus Signus's Outpost on the bookshelf (the location of Hermaeus Mora's quest) or at the Abandoned House in Markarth (the location of Molag Bal's quest), or, after completing House of Horrors, one of Boethiah's followers will attempt to assassinate you- they will be holding Boethiah's Proving. Alternatively you may be randomly attacked on the road by a follower who will have the book in their possession and reading it will start the quest without completing any specific mission.

One of Boethiah's followers will speak to you and ask you to lead someone to sacrifice- you will also be given the Blade of Sacrifice at this time. Any can be taken to the Pillar of Sacrifice to be killed, except for essential characters or any of the dog companions. You may want to hire a stranger in a tavern, or you can invite brawl followers if you want to save money. Bring your chosen victim to the Pillar and tell them to use it, they will then be sucked to the pillar, allowing you to kill them. You can also kill all of the followers near the Pillar of Sacrifice, in which case Boethiath will ask you to do the same by using the last follower you have killed. If you have the Ebony Blade, now would be a good kill to use it on.

Boethiah will use their body as a conduit- the body will stand up after death and speak in Boethiah's voice- after listening to her and following her downstairs, you will be forced to fight each and every one of Boethiah's followers. However, they will also fight amongst each other, so if you are having difficulty, you may want to let them kill each other and then finish off the rest. After defeating them, Boethiah will use the last person you kill as a conduit and tell you she is bored of her current champion, who now runs his own gang. You must then travel to Knifepoint Ridge and kill them all silently.

In order to kill each one silently, you should either hit them at long range with a bow, or jump off the walkways to land right behind them one by one and kill them from behind. In order to defeat Boethiah's champion without him noticing, you can jump on top of the boxes behind the house he is in, and fall through the hole in the roof. He is wearing the Ebony Mail, but the poison effect does not begin until he notices you, in the same way the poison effect does not begin as you wear it until an enemy notices you. Once he is defeated, loot the Ebony Mail off his body and wear it- Boethiah will speak to you one final time, and the quest will end.

Whether or not you kill the enemies at Knifepoint Ridge by using stealth attacks or by just rushing in and tearing everyone down, the quest will complete the same way with the same dialogue after you kill the Champion of Boethiah. There's no special reward or extra dialogue to be obtained from killing all of the enemies using stealth.

A video walkthough is available here

Bugs

 * Sometimes after killing the follower on the pillar, Boethiah's conduit will not start the dialogue with the player, making the quest impossible to continue. To fix this, just kill all of her worshippers. Then she will leave your companions body and go to the last worshipper you killed. Then you can actually talk to Boethiah's reincarnation and continue the quest as usual. If the dead worshipper she repossessed still does not engage in dialogue with you, and give you the next quest update, reload, kill all the worshippers, and THEN take your follower up to the pillar and have them touch it. Even though she has already possessed a dead worshipper, this will kick-start the quest, and will result in a double dialogue update stating you've sacrificed a follower. (Xbox/PS3/PC confirmed).
 * If you proceed to do the above suggestion, and Boethiah asks you to make another sacrifice to her with a thrall, the sacrifice will not work, rendering the quest incompletable.
 * If you cleared out Knifepoint before you get this quest, it is possible to have the quest not move past the stage where it is telling you to kill everyone. If this happens, you may be able to move the quest along by putting on the Ebony Mail you get from killing the leader, but this does not always work.
 * There should be more targets outside the mine at this point; eliminating them and then putting on the Ebony Mail triggers Boethiah's final dialog and quest completion, but leaves the quest objective "Slay everyone at Knifepoint Ridge stealthily" unfinished. (Had the same issue; this fixed it. Confirmed PS3)
 * If you open your journal while Boethiah is in possession of one of your companions, or one of her followers, it is possible for the visual effect to never end. Reloading an earlier saved game will fix this.
 * If you have lost your follower somewhere in the world you won't be able to get a new one thus preventing you from completing this quest. I was able to remedy this by doing some quests for the Companions. I recieved a message 'your companion replaced your follower'. Finish your companions quest then go grab a follower and sacrifice them.
 * Sometimes, as you sneak onto the walkway further in the cave, the champion will attack the bandits. This results in far less work to complete your task. Letting this play out and picking off the remaining enemies does not seem to negatively effect the mission in any way. (Xbox 360. PS3 Confirmed)
 * Sometimes Boethiah will offer no interaction with the player. It is best to reload. (360)
 * If you lure an enemy to kill the cult of Boethia for you, (A frost troll in my case) the cultists of Boethia will not retaliate, and the two fighters in the arena will become glitched, and cannot be attacked or talked to. None of the cultists will attempt in any way to kill the enemy, and will not retaliate when you try to attack them. Nor will they say anything, and this will make the quest impossible to finish.
 * If your companion is wearing a dragon priest mask when they are sacrificed then it cannot be recovered once Boethiah is finished possessing your follower.