Amnesia: The Dark Descent is a historical psychological survival horror game that was developed by Frictional Game. It was released on September 8, 2010 for Steam, and February 11, 2011 for retail.
PewDiePie did a let's play of Anmesia: The Dark Descent that consisted of 34 episodes, which started on December 25, 2010 and ended on January 24, 2011.
In late August in the year 1839, Daniel, a young man from London, awakens in the dark halls of the Brennenburg Castle with little to no memory about himself or his past. All he can remember is his name, and that he lives in Mayfair and that something is hunting him. Shortly after awakening, Daniel discovers a note written to himself, from which he learns that he has deliberately erased his own memory, and that he needs to descend into the Inner Sanctum of the castle to kill the Baron, Alexander.
The exploration of the dark depths of the castle (following a trail of pink liquid that he seems to have left for himself,) is also a journey into his own erased past, as he discovers not only notes and his own journal entries, but experiences visions of past events that took place within the castle's countless chambers (including memories that are not his own). While he unravels the mysteries of Brennenburg Castle, he also finds himself hunted by a dangerous unearthly presence that manifests itself as a corruption that is slowly covering the castle in fleshy, acidic growths, and bizarre monsters against which his only defense is to flee. These events are linked and pertain to why Daniel came to Brennenburg.
Daniel was once a part of an archaeological expedition to Africa, in an attempt to excavate a tomb called "The Tomb of Tin Hinan." He came across a mystical orb buried within the ruins of the ancient temple, and brought its broken pieces back to England where he successfully assembled them. Daniel started to seek information about the Orb's history from a geologist and a professor.
However, he began to be plagued by nightmares, and several people who came across his path, and that of the Orb, died horribly at the hands of the "Shadow" that appears to dog his footsteps. Desperate and despairing, he received a strange letter from a Prussian baron named Alexander, who promised protection if Daniel would sojourn in his castle.
Daniel had no other choice but to flee to Brennenburg. As he arrived at the castle, he was greeted warmly by the baron, Alexander of Brennenburg and his servants, who appeared to be very pleased by Daniel's arrival. But the young man was unaware, the enigmatic deity had silently chased him to Brennenburg. Alexander knew this, and promised Daniel that they will banish the cosmic beast forever.
Alexander told Daniel all he knew about the Orb's power. Daniel doesn't seem to be interested about the artifact's true nature and suggested that they should throw it away. Alexander advised against that as Daniel would still be a part of the Orb, and eventually be consumed by the Shadow. Having the Orb, he could still fight back. Daniel asked Alexander about the letter he sent to respond Daniel. Alexander simply said, things can be done, but at a price.
Alexander showed various parts of the Brennenburg castle to Daniel, including the archives, a refinery, a prison where he kept the "criminals," a bottomless pit called the Chancel, and the Inner Sanctum itself, where they can permanently banish the Shadow.
During their visit in the Inner Sanctum, Alexander began to tamper with the Orb, thus enraging the Guardian, whose fleshy residue appears in the Sanctum. Alexander quickly covers the Orb and the Shadow disappears. He tells Daniel that they have very little time to banish the Shadow. They must quickly start the Warding Ritual before it's too late.
However, Alexander's promise of salvation was a lie. He is actually an otherworldly life-form who has spent centuries in Brennenburg, attempting to open a "gate" back to his own world. To do this, he needs a substance called "vitae," which can only be harvested from the blood of agonized humans. He also needs a usable Orb. As such, Daniel is a boon to his efforts: Alexander employs him as his personal torturer, replacing his former servants who become the monsters Daniel flees from, and claiming that the vitae will fuel a ritual to banish the Shadow from Daniel's presence forever. Daniel initially embraces this role, particularly when Alexander tells him that the humans he is seizing are vile criminals. In order to produce enough vitae, Alexander and Daniel feed the prisoners they torture with an Amnesia potion, which makes them forget the method of their torture, and ensures that they will be just as terrified the second time around, without becoming accustomed or resigned to the pain (the Damascus Rose is alluded to as either one of the ingredients of the Amnesia potion, or as a flavoring that Daniel perhaps added to the mixture to disguise its taste.) As the experiments continue, however, Daniel's faith in Alexander is shaken, and finally shattered when he murders a little girl in cold blood following her escape from a prison cell.
Alexander saw that the event had taken a toll in Daniel's mind. Taking the Orb with him, Alexander sealed himself in the Inner Sanctum, leaving Daniel to be brutally maimed by the cosmic guardian.
Despondent over how far he has come, and furious at Alexander's trickery, Daniel chooses to drink the Amnesia potion himself so that he can atone for his sins without the burden of crippling emotional trauma, leaving but a note to his new self to murder Alexander.
The new Daniel found the note his former-self left, telling him to kill Alexander, but also to escape the approaching Shadow as long as he can. Then he came across a lantern, which he carries with him. As he started to travel in the castle, he realized that his former-self warning was right. This beast, the Guardian of The Orbs, dogs his footsteps, as do the terrible monsters patrolling in the corridors of Brennenburg.
Daniel eventually manages to find the Inner Sanctum buried deep below Castle Brennenburg. He breaches its defences with a newly assembled Orb and the help of Agrippa, an alchemist that Alexander has kept imprisoned in Brennenburg for centuries with the use of strange alchemy. Agrippa, who once studied Orbs with his student Johann Weyer, explains the purpose of the Shadow: it protects the Orbs, slaying anyone who threatens to abuse their power. He mentions also that Weyer managed to travel to Alexander's world using the power of the Orb, and begs a favor: that Daniel separate Agrippa's head from his body with the help of a tonic that will ensure his head will remain alive, and then take it with him.
There are three possible outcomes to the confrontation with Alexander, depending on Daniel's actions at the Inner Sanctum: he can fail to prevent Alexander from returning to his home world and get killed by the Shadow and trapped in eternal darkness, though Alexander thanks him for his sacrifice, and tells him that what he has done will not be forgotten and he will be celebrated forever; he can destroy the device creating the Gate, managing to escape with his life, and says that he was content to be leaving Brennenburg having redeemed himself and knowing that Alexander has paid the price for his sins; or he can follow Agrippa's advice and toss his head through the portal. If he does, Daniel is still killed by the shadow as well as Alexander. However, Daniel is saved when Agrippa finds Daniel saying that he deserves so much more and calls upon Weyer to help him save Daniel, promising him that "everything will be alright."