Daniel cannot fight back against this living nightmare nor hope to hide from it. All attempts to banish it have failed: all Daniel can do now is flee from it for as long as possible.
Where the Shadow passes, it leaves behind a fleshy organic "residue" that is harmful to touch. If Daniel is too close to this residue, his sanity will slowly decrease. Sometimes, Daniel has to jump on this residue in order to advance through certain parts of an area.
As Daniel progresses through objectives and travels deeper into Brennenburg Castle, more of the fleshy substance is visible because Daniel is getting chased by this so-called "demon". The residue can be seen pulsating and can have human skulls, parts of rock, and occasionally whole limbs embedded inside of it.
The flesh itself is unnaturally strong and elastic, it cannot be damaged by tools or brute strength. Only certain types of acid can dissolve a thin webbing of it, though given time will regenerate as the Shadow's influence intensifies. When it corrupts the Back Hall it turns the water from the fountain into blood. The Shadow's more sudden appearances are accompanied by violent shaking and loud echoing roars.
Although it is likened to a "beast", the Guardian actually demonstrates that it is very intelligent. It pursues Daniel quickly as the young man tries to escape it, whereas when it finally has him cornered it'll slowly advance on him, taunting him, almost savoring the moment as it closes in for the kill. It also knows about Daniel's fear of the darkness and will often blow out or obscure all sources of light as it passes, but Daniel's oil lantern is helpful for all situations. The Shadow notably hates Daniel having high sanity and will often roar just to lower it.
Though the Guardian safeguards the unnatural power of the Orbs from thieves in order to protect the Universe, and has killed many people to achieve that end, it may spare some robbers' lives. When Agrippa discovered his first orb in the Prussian forests, near Altstadt, he was caught by the Shadow but not harmed. It reclaimed the Orb and carried the man miles away across the Alps to a grassy field outside Genoa. It's ultimately up to this otherworldly force's discretion if the victim is mutilated, or completely devoured.
Johann Weyer was the only one since the fall of the Mithraic faith who managed to assemble an entire collection of orbs and separate the living nightmare, that is the Shadow, from them. He could use their power without incurring the cosmic beast's wrath, but he had very little control over the Guardian itself. In 1558 he was able to summon the Shadow within an Orb Chamber in Calais to consume some murderous French soldiers so he could claim the mystic relic they had found, but he could not then stop it from swallowing up everything and everyone around it and had to flee.
At the beginning of the game, the Shadow was pursuing Daniel because he had taken an Orb that resided in an African tomb in Algeria. Though the young man was not directly harmed everyone else he came into contact with was brutally killed afterwards. In order to seek refuge from this ancient horror, Daniel travels to Brennenburg Castle, where the baron Alexander promises a means of warding off the Shadow.
Alexander repeatedly mentions that Daniel is "tainted" and "branded" by this supernatural force. The meaning of these labels concerning the young man is not understood, as Baron was intentionally being cryptic. To 'taint' something is to contaminate it, whereas 'branding' someone is to mark them indelibly, indicating ownership. Whatever he was implying it is certainly obvious that the Shadow knows exactly where Daniel is and is never far behind.
It will not allow Daniel to escape it via the portal Alexander creates in the Orb Chamber, because he's "branded" so the cosmic force literally "owns him". It causes the young man pain whenever he tries to pass through the gateway himself. Alexander coldly states it makes no difference, even if Daniel could travel beyond the Universe, it would still inevitably catch and consume him either way.
Occasionally The Shadow roars when Daniel does certain things, like making progress or entering a new area, the castle shakes but the red residue does not appear. It will constantly hinder his progress, blocking the most direct route to Alexander. If Daniel tries to leave the castle via the Entrance Hall in the beginning of the game, however, red flesh covers the door, preventing his escape.
It proves itself to be unstoppable in its hunt for Daniel. From the towers of the castle, to the toxic Sewer tunnels and the bottomless pits of the Chancel, no environment deters or hinders its expanding organic matter. It works very similar to the gameplay mechanic of an "advancing wall of doom". Its organic matter even expend outside the castle itself, the forest can also seen covered by fleshy matters.
While this fleshy residue is easily seen even in the darkest reaches of the castle, there is no mention of it before Daniel arrives in Brennenburg. In the journal entries the Shadow is described as a completely invisible force. A bright red aura is often radiated when large masses of flesh join together. Also, though this residue is known to be left by the Shadow, the being itself is never seen. It is unknown if it has physical form at all. All that can be assumed is that the ancient horror is gigantic. The stomping noises made as it chases Daniel gives a feeling of its immenseness. The movements it makes when following Daniel cause all of Brennenburg Castle to tremble. It makes the ground quake, and fells tall trees. It also makes the castle start to cave in.
The Shadow hounds Daniel and thus is constantly confronted throughout Brennenburg Castle. It is responsible for the unnatural darkness that shrouds the rooms in Storage. If Daniel lights some candles it will randomly roar causing the entire environment to go darker still. Any lit candles and his own lantern will also glow with an eerie dark red.
The "demon" blocks Daniel's escape from the Entrance Hall and initially his progress until acid is created and utilised to erase a thin webbing of the Shadow's residue that is blocking the path to the Refinery.
Curiously, this supernatural entity interacts with the monsters it comes across differently. When it consumes the Cellar Archives and Cistern, it allows the Kaernk to appear and attack Daniel. Without its influence and flooding the cellars, the water monster wouldn't have been able to even pursue Daniel in this area. Whereas with the Gatherers, a Servant Grunt was seen lying in a bloody mess somewhere in the Sewers. It is possible that this was the work of the Grunt's fellow Gatherer, the Brute, which was in the same area and may have used the blade on its arm to hack the Grunt into pieces. While Grunts are shown to work together when commanded to do so, it is unknown if a Brute would tolerate them, much less cooperate with them. If the Brute was not behind this attack, however, it is to be speculated that the Shadow itself tore Alexander's servant apart.
When Daniel repairs the machine that powers the elevator in the Back Hall he enters the lift just as the Shadow swallows up the entire area. The guardian advances through many floors, and overtakes the shaft as it tries to stop him. However, the cables snap in the process and the elevator plummets down to the Prison before it can consume Daniel.
Interestingly, if Daniel waits too long in the Cistern, the Shadow unintentionally allows him to escape this area. While it does block the normal route of escape and summons another Kaernk to contend with, its flesh actually forms a "bridge" leading out into the next room that Daniel may walk over safely.
If Daniel falls back down the well he climbed out of to reach the Nave, he will respawn in a room that's locked off at first from the outside. Upon trying to leave this room, The Shadow consumes it, thereby briefly blocking the only exit door with its organic residue, then removes the residue off the door to allow Daniel to leave.
Although described as "sluggish", the Shadow can occasionally move much faster than normal. When Daniel escapes the Cells, a tense pursuit between Daniel and The Shadow is initiated and the red residue appears at a much quicker pace. Should Daniel cover a lot of distance the guardian will advance even quicker, only slowing down a little when it comes across shallow water. Being caught during the chase means immediate death.
The Shadow bellows angrily when Daniel completes Weyer's Tonic for Agrippa. It does not want the young man helping the dying alchemist, knowing full well it would mean Daniel has to abuse its orb's power to help another.
When Daniel enters the Inner Sanctum to confront Alexander, another tense pursuit between the young man and this cosmic persecutor commences. Fortunately, Daniel is able to slow it down by closing a huge door buying him precious time to break the final seal to the Orb Chamber where the Baron waits. The Shadow overtakes the area with its organic matter and roars angrily when Daniel leaves the area.
The Orb Chamber marks the final encounter with the Shadow in the Dark Descent, one that will result in three different endings depending on what Daniel decides to do next. Allowing the ritual to take place, either by doing nothing and watch Alexander escape, or throwing Agrippa's head through the portal will result in him being consumed by the Guardian.
Furious with him for either allowing another to abuse his orb's power, or misusing it himself, the cosmic force devours him. Daniel's consciousness is sucked inside the Shadow, a dark void, where the only sound is the sickening squelching of the beast's fleshy matter. If Daniel decided to save Agrippa, he asks Johann Weyer to work on a way to save him, as heavenly lights appear beneath the Shadow. If not, Daniel faces the cosmic guardian alone without any hope of escape and his worst fear is finally realized as he's trapped forever inside its absolute darkness.
If Daniel chooses to stop the ritual, the Shadow will overtake the chamber. Alexander's escape-bid is foiled and he screams that they're both going to die. However, the Guardian is appeased by the length and effort that Daniel went to stop the Baron from misusing the Orb. It will not roar at him or frighten the young man by blowing out all the lights. Even its organic tissue doesn't hurt him to touch. The Shadow spares Daniel, and for his earlier transgressions, only devours Alexander as atonement. No longer hunted, Daniel is free to leave Brennenburg with a guilt-free conscience.
- One of the Loading Screens states it is not some "vengeful spirit" but the very Universe catching up and trying to contain the Orbs. If this is true, the manifestations of its fleshy matter imply the very cosmos that Daniel and everyone exists inside of is actually alive and sentient. It maintains itself, guarding the Orbs and hunts down whoever seeks to use them because if they try to leave it, that is the Universe, these "escapists" may threaten its stability.
- The religion Mithraism seems to be connected to the Orbs in some way, so it is possible the Mithraists believed the Shadow was either their god Mithra himself, or the giant bull being slaughtered in the iconic scenes monuments of which Zoroastrianism interpretations depict him or another deity slaying the primordial bovine Gavaevodata whose fleshy matter becomes the progenitor of all life.
- It is not explained how the Orbs contain their unnatural power, or why the Mithraists could invoke them without getting hunted and killed by the Shadow. Weyer and Daniel (temporarily) were able to use the Orbs without incurring the Guardian's wrath. Its possible the Orbs choose their holder. Or maybe the Shadow deemed them worthy of handling such power, but not Alexander, Agrippa or Herbert, who would likely use it for their own advantage.
- Daniel may be "branded" or "owned" by the cosmic guardian simply because he touched the orb and by doing so, became "tainted", inadvertently invoking the relic's powers and channelling them into himself. This might be why his intuition is so high and how he can recall foreign memories not belonging to him. The Shadow may now regard Daniel as much of its possession as the mysterious artifacts it usually guards, hence why its so obsessed with him that it would kill anyone who dared make contact with him, and even ignore the two orbs currently residing in Brennenburg, making no attempt to recover them.
- While the Shadow is hunting Daniel relentlessly throughout the game, it is plausible that the nightmarish force originally had no intentions of harming Daniel, even though he took one of its orbs from the archaeological expedition to Africa. It did not actively hound him down to start with, merely content with following behind its orb carrier.
- Why the Shadow didn't simply take back the orb or dispatch Daniel as soon as he left the burial grounds is unknown. It's possible it chose the young man to wield the orb as it saved his life in the tomb. It could have also spared Daniel in the beginning since he did not take the relic to wield its otherworldly powers for personal gain (indeed, he was oblivious to them) but simply to preserve it in a museum. He also did not remove the orb from the burial grounds, he was unconscious and forcibly carried away by Herbert's men with the broken orb shards in his hands.
- In the Choir Daniel is taunted by Alexander via telepathy who tells him he's responsible for all the deaths because if he had only "submitted to the Orb" when he first discovered it none of the bloodshed in Brennenburg would have happened. If true, if Daniel had not tried to flee from it but merely accepted the Orb's Shadow and yielded to it's superior will, the events of The Dark Descent would not have occurred.
- Daniel spellbound by dreams, fell overboard from the SS Hortensia headed for London. Beneath him in the dark Atlantic waters something very large tried to take him away. The current caused by it moving pulls him underwater and Daniel nearly drowns, but then he is raised up and put back onto ship, by what he doesn't know. The crew of the ship did not respond to his distress. It happens so calmly that he wonders if it was all another dream. This unseen beast may have been the Shadow making an attempt to abduct him, and then abandoning the course of action.
- There is no explanation given for why the Shadow did not consume Daniel in Africa or during his stay in London. It could have easily done so at any point. Herbert recovering the second orb may have served as a distraction initially, but it wouldn't have taken it long to catch up to Daniel who eventually arrived back in London on the 22nd of June 1839. The Shadow only mercilessly murdered those who Daniel contacted enquiring information about the ancient relic, it made no attempt to take Daniel's life. When he learns about Professor Taylor and Sir William Smith's fate, Daniel immediately jumps to the conclusion he's next. Fearing for his own safety he flees on 17th July 1839, but does not once rationally consider that he's been staying in the same area for 25 days and yet no harm befell him during that entire length of time.
- Given that Daniel was not himself attempting to study the orb, merely asking others to do so, it could be that any attempt whatsoever to harness the orb's powers, including simply studying it, is enough to provoke the Shadow. Seeking Alexander's help and performing the "warding rituals" could perhaps be seen as attempts to use the orb, thus ironically bringing the Shadow's wrath upon Daniel.
- After taking the orb Daniel's sleep was strangely plagued with nightmares, as if a voice were calling across the void. The vivid dreams enabled Daniel to rebuild his orb. This may have been the Shadow's early attempts to communicate with him.
- If the Shadow was trying to use nightmares to converse with Daniel, it would explain why it murdered Dr. Tate despite Daniel not taking the orb along with him, or discussing it. His physician simply gave him medication to stop these frightening dreams. His interference no doubt antagonized the monstrous force. Evidently as it killed him within 48 hours, whereas it gave the marked Prof Taylor and Sir William Smith each over a week to live. On the other hand if The Shadow regards the "branded Daniel" as its property, the doctor simply examining him for a check-up would anger it in much the same fashion as inspecting its Orbs.
- It is possible Alexander provoked or angered the Shadow thereby deliberately turning it against Daniel, since it was merely content to slaughter only those Daniel had been in contact with. When Daniel fled to Brennenburg, he believed that Alexander would protect him from this force and convinced him they can banish the guardian of the orb. However, on 8th of August 1839 Alexander tampers with the artifact, Daniel has no idea what he is doing with the strange tools. Suddenly the invisible force around Daniel now materializes, and the walls burst with pulsating tissue. After this point the Shadow is notably enraged, it roars and cries constantly, and now threatens to consume the entire castle and Daniel along with it.
- Why Alexander would risk the guardian's wrath is unclear, he may have attempted to simply tame its power or intentionally doom Daniel in order to usurp the orb's power from him and add its energy to the one he took from Agrippa. Either way, it now threatens Daniel giving him the incentive to cooperate fully with the baron since the Shadow is brought out in full-force and is actively hunting him. The blood wards Alexander has Daniel perform cannot banish it. These only serve to distract the guardian's blood-lust and anger it further. It could even be holding Daniel personally responsible for allowing Alexander to invoke its orb's power and why it'll devour him in three of the four possible endings.
- When Daniel is imprisoned in the Cells, the Shadow realistically gives him plenty of time to escape. It does not appear for some ten minutes. It eventually gets angrier and angrier if Daniel stands idle, and refuses to leave. If Daniel leaves the cell, its spread stops immediately. Only when Daniel escapes the chamber does it give chase. This can be interpreted that the Shadow if anything, wants Daniel to stop Alexander, and is "hurrying him along", willing even to give him a head-start should he stupidly get caught first-time round, because being ambushed by the Gatherers has wasted a lot of precious time needed to stop the baron. Its fleshy matter manifesting behind Daniel can only signify the entity is not "hunting" but forcing him to go forward, its advancements remind him there is no turning back from this dark descent. Any reluctance on the young man's part to defy Alexander's expectations enrages the "relatively-patient" guardian.
- Only when the Shadow absorbs the Chancel does one of Daniel's diary entries appear. Its the one marking his downfall as he realises what he has become after murdering Zimmerman's innocent daughter. By bringing it back The Shadow may be forcing Daniel to relive the crippling guilt of his former-self's actions, specifically the awful memory that old Daniel couldn't bear to live with before taking the Amnesia Drink. Also, in the 'Bad Ending', it may be haunting him with the awful memories of all those he tortured to death in Brennenburg.
- The Shadow's claim on Daniel also provides a plausible explanation for why Daniel resurrects whenever he is killed by one of the monsters in the castle (unlike Justine, who only has one life). The Shadow has no intention of letting Daniel die, wishing only to "hold his feet to the fire" via terror, and make him "experience purgatory". This is showcased when it taunts Daniel should he fall down the well in the Nave when it intentionally traps him in a sealed room, then releases him. The entity wants to see whether Daniel's intentions with preventing Alexander misusing the orbs, are meet with its approval. Alexander may also know this, hence his determination to quash Daniel's resolve - he can't permanently kill Daniel if the entity keeps reviving him, so he wants Daniel to give up so he can escape unscathed.
- In order to use the orb long enough to perform the ritual without being killed the Baron may have turned Daniel into a sacrifice for the Shadow. Alexander hints at this several times, saying that "things can be done, but at a price" and urging Daniel to offer himself up. It might offer another explanation for the entity's strange behaviour, since it is hounding Daniel, but ignoring its orbs.
- If Alexander did infuriate the Shadow this would explain why it only killed him in the 'Revenge Ending', and left the 'redeemed Daniel' completely unharmed.
- In the 'revenge ending' Daniel flees Brennenburg, but it cannot be certain if the shadow has departed forever, or turned back into its original "invisible-state" prior to Alexander's meddling. What is interesting is that castle Brennenburg collapses once Daniel leaves and not before. Whether this was the Shadow's doing, i.e. waiting for him to get to a safe distance, or purely coincidental is uncertain.
- A strange red aura is visible around Daniel as he walks back out through the castle. The guardian may be following him again since Daniel is still "branded" or because it cannot reclaim its stolen orbs back, as they've already evaporated away.
- Alexander was the one that named the enigmatic Guardian of the Orbs as "The Shadow".
- The cosmic nightmare moves much faster outside Castle Brennenburg than inside the thick walls. The structure is the only thing that is slowing down the surrounding Shadow and preventing it from instantly swallowing up the helpless Daniel.
- It would appear that the refinery is the first place in Brennenburg where the shadow manages to break into. This is first area where the fleshy matter appears and several large holes appear above, looking as if it bored or burrowed its way deep into the castle.
- Shadow can assume an "invisible form" if it wants to. There is no mention of the supernatural entity's fleshy residue according to Agrippa and Herbert in the journal entries. It can only be heard roaring or baying and can only be 'seen' as it interacts with the environment.
- Throwing objects into the flesh-covered walls such as crates or bottles can result in them either being lodged in the organic matter or hurled back out with great force. If pushed into the pulsating matter, The Shadow can easily destroy these large crates and unbreakable big bottles that Daniel may find lying around.
- It takes almost three minutes for Alexander to complete his ritual and then the Shadow slowly arrives to kill Daniel, but if Daniel disrupts or stops the ritual the Shadow invades the Orb Chamber almost instantly.
- In the bad ending the guardian kills Daniel much slower than Alexander in the other endings. Although should he abuse the orb himself and save Agrippa in the 'special ending' the entity will engulf him very quickly.
- In the 'revenge ending' all traces of the Shadow's fleshy residue vanish.