Duality (dungeon)

Duality is a Dungeon that was added to Destiny 2 in the Season of the Haunted. It revolves around Eris Morn sending a fireteam into the mindscape of Calus, only to find it a schism overrun with his Nightmares. Guardians must fight through the shame haunting the emperor to steal knowledge from the deepest parts of his consciousness.

Walkthrough
To begin your journey deep into Calus' consciousness, move onwards through the Tribute Hall to the large statue of Calus. You'll find Eris Morn, who will brief you on the mission. After she is done talking, the floor surrounding the statue will disappear, allowing you to fall into the Mindscape.

Navigate the Mindscape
You'll land in a room with a gate ahead, bright light filtering through. Move up to this gate and look straight ahead. You should be able to see a bell-like construction. Shoot this enough to be transported into the Nightmare realm of the Mindscape. Within this Nightmare realm, continue towards the bell you shot, and once you're within close range of it (close range as defined by the circle around the bell, on the floor), shoot it again. This will teleport you back to the normal realm. Standing outside of this circle and shooting the bell when within the Nightmare realm will cause you to die when the realm shift occurs.

Now, back within the normal realm, turn around and you will find various Cabal units spawning. Kill them, or ignore them. Move to the other end of the room from the bell, and begin platforming upwards throughout the room, using the struts spanning between the pillars to climb. Beware the Psion snipers positioned on the ledges around the edges of the room. Once at the top, look to the opposite end of the room for another bell. Shoot this to enter the Nightmare realm. Cross from this side of the room over to the bell on high, and use it again to shift realms. Once more, continue into the new area and engage or ignore the Cabal enemies. On the left-hand side of the room, you'll find another bell through a gate. Use this to shift into the Nightmare realm, and walk along the left edge of the room, until you find an open entrance in the wall. Continue inside, use the bell you last shot to shift realm again. Once shifted, look to your side for a gap. Fall down to the bottom, careful not to break your ankles, and then look through the gates towards the opposite side of the room. You'll see another gated bell. Shoot this, shift realm, hop through the gap in the wall, cross to the other side, hop in the hole in the wall and follow the platforms to reach the bell you last shot. Shoot this to shift realms again, and then fall down the same type of gap in the floor as previously. Continue following the path until you reach a doorway that looks like a big open mouth, with its tongue lolling out. The room will be filled with Cabal enemies, so get in there and clear them out. Once they've all been killed, you'll find that a doorway in the middle opens up, allowing you to progress to the first boss, the Nightmare of Gahlran.

The Nightmare of Gahlran, Sorrow Bearer
Once you land, you should find a rally flag deposit point. The layout of this arena can be considered to be symmetrical. At both ends, you'll find a bell, with currently-closed doorways to their sides. You'll see a projection of a familiar Leviathan symbol in front of each of these doors. Chalice and Sun will be next to the bell located up the small set of stairs, Axes and War Beast will be next to the other bell.

To begin this fight, shoot the bell to shift into the Nightmare realm. Once inside, the Nightmare of Gahlran will be present and invulnerable, so try to ignore him while he chases you. Lots of other Cabal units will spawn, with a pair of sniper Psions located on far-out pillars, guarding each bell. You will also find two Nightmare Bellkeeper units at the opposite bell from which you shot, and these must be killed to allow the bell to be used again for a realm shift. When within this fight, you can only spend a limited time within the Nightmare realm (indicated by the ticking-down debuff on the buff list), before it collapses on you. Collapsing means anyone there will be killed. This means you need to kill the Bellkeepers to provide you with an escape route via the bell.

Your objective within the Nightmare realm is to kill Standard Bearer Psions, which will drop an appropriate Standard for you to deposit back in the normal realm. These Psions will spawn in the rooms behind where the projections were in the normal realm. Use your radar to help you locate which one of the four rooms you will find them within. Once killed, scoop up the Standard and get back to the bell. Keep in mind you can carry more than one Standard at a time, but dying will cause you to lose all carried Standards, meaning you will have to shift to the normal realm, then back to the Nightmare realm, to collect more. Killing a Standard Bearer will provide you with extra time within the Nightmare realm.

Once you have shifted back to the normal realm, find the deposit point for the Standard you carry and deposit it. Doing this will open up the room behind the deposit point, containing a Cabal Colossus and some War Beasts. Kill them to clear out the room, ensure the Bellkeepers have been dealt with, and while standing inside the newly-opened room, shoot the bell to shift to the Nightmare realm.

Once done, you'll now be inside a previously inaccessible room, with a collection of Visions of Gahlran. Kill all of these within the room you're contained within, and a doorway will open at the opposite end from where you warped in at. If you have cleared out all Visions of Gahlran (on both sides), ensure you snag the Nightmare Essence dropped by killing a Vision before leaving, and prepare to engage Gahlran himself. As he is a melee-based foe, it is advised to use weaponry you can use at close range here. Using a rocket launcher or grenade launcher will lead to disaster. Keep a close eye on how much time you have left in the Nightmare realm before it collapses. Once you're low on time, use the bell to shift back to the normal realm and repeat the process to allow damage to be possible again. Take note that Nightmare Bellkeepers still exist, so taking care of them before Gahlran is prudent.

Once defeated, loot spawns in a chest next to a newly-opened hole in the middle of the room.

Dive Deeper
Now for another extended platforming section. Fall down the hole into a room full of hardened Royal Wine, jump up onto the surrounding ring ledge and take either the left or right path out of the room. Continue going down, down and down until you reach a set of pipes connecting and leading you to a bright light. Follow this, and you'll arrive in a room with a large abyss. There will be some Cabal units to deal with directly to left. Fall down to these, kill them, and jump across the gap to the other side. On this, you'll find a switch, which when activated will produce some platforms on your side of the room. Follow the newly created platforms, hop the gap to reach the side you originally came from, and you'll reach another switch. Activate this, and then return to the other side of the room, where platforms have been newly produced again. Kill any enemies in your way and continue your climb, until you find an opened doorway you can pass through.

Passing through this doorway will put you inside a long diagonal passage, which you will be forced to slide down at high speed. Kill your speed just before you reach the bottom (jump, air dodge, sword swing, etc), or you'll end up dead. To your left upon landing is the route forward. Continue through the passageways to reach a similar room to the last, with a platform you need to climb onto to continue. Follow the ramp from it, through the passageways, until you reach a dead end. Just before the dead end, on the left, is a gap in the wall. It appears to be another abyss, but far in the distance is your objective, a thin gangway that leads to the next area. Jump and land upon this. Proceed through the tiny hallway on the right of this gangway, until you need to jump up out of a cylindrical area. Hop through the doorway and into a large room with 4 gladiator statues surrounding a central bell.

This room holds a simple puzzle. All the statues need to point to the middle to unlock the way forward. To rotate the statues, you need to use the bell to shift to the Nightmare realm, which will then make visible switches at the far-side of the base of each statue. Using these switches will rotate the statues 90 degrees each time, though the rotation is only visible in the normal realm. One statue is already correctly rotated, and the other three incorrectly. Two of them require two turns to align, and one requires three. Take note of which statues need to be rotated, assign placements for your fireteam, and begin the turning after shifting realm. Once done, shift back to the normal realm. If successful, the floor beneath the bell will begin to unlock, revealing the way forward.

Unlock the Vault
After falling down the doorway that opened beneath the bell, you will find yourself in a new room. Stepping down the stairs on any side will begin the fight, so be aware of this. There will be a rally flag spot close to the bell that isn't up a set of stairs.

The layout of the room is as such. There are 6 Standard deposit points, arranged in a circle in the center of the room. Two bells will exist at opposite ends of the room, one up a set of stairs, another on the same level as the deposit points. To the left and right of the lower bell, respectively, are the Sun and Chalice Standard points. To the left and right of the upper bell you will find the War Beast and Axes Standard points. The large dividing wall segment located in each corner of the room will have a large relief on it, to indicate what symbol is associated there. Bellkeeper spawn points will be located on a level just below the bells.

Your objective here is to place the required Standards, and once two have been placed, a Nightmare of Calus' past will become vulnerable and must be killed. Once dead, a new Nightmare will spawn, and you will need to collect two more Standards to make this new one vulnerable. Once this one is dead, another will spawn, and the final two Standards must be placed to make the final Nightmare vulnerable. Once this one has been killed, the fight will end.

To begin, step off the main circular dais towards any of the Standard points. Enemies will spawn in great number, and you will see projections of symbols in the middle to indicate your targets. Kill Bellkeepers, and ensure you know which direction to head in for Standard acquisition. Shoot the bell, and you'll shift to the Nightmare realm. Once inside, head up the newly created staircase for whatever Standard you need to find an area with a selection of Cabal enemies. Kill all enemies in this area, including the Colossus all the way at the back, to then spawn the Standard Bearer Psion. Kill this Psion to produce the Standard you need, and provide extra time for you to be in the Nightmare realm. Avoid the spawns of War Beasts that occur once the Standard Bearer appears, and head back to the bell with both Standards. Kill the Bellkeepers (they always spawn opposite the bell you need to use), and shift back to the normal realm. Deposit both Standards and set about the Nightmare until it is dead. Now repeat this another two times and you're finished.

Navigate the Vault
Upon victory, the floor in the middle will unlock, opening up a way forward. Fall down to find your loot chest. Behind the chest is your way forward. Follow the path, then take a left or right to continue. You'll eventually reach a large room with a shrouded object in the middle. On the far left side, you'll see a bell through a familiar gate. Shoot this to shift to the Nightmare realm once more. Kill the Cabal units in your way and proceed onward to your right, jumping the gaps and using the struts to move. You're looking to use one of the gap doorways on the right hand wall to proceed onward, which will lead you to a bell. Shift realms, and then climb upwards from this room, following the ramp, up and up, to another gate. Shoot the bell on the far side of the room, shifting realm, then cross over to the bell to shift back. From here, jump out to your right hand side to find some platforms and Cabal. Continue on to cross to the other side, where you'll find another doorway leading to along diagonal slide. Break your fall before the end to survive, and move onward to your right. Keep an eye out for ledges sticking out on the right hand side of the wall in this huge open room, as that is the path forward. Eventually you'll see a gap in the wall on the other side, emanating light. That's the final room of this dungeon, so head over there.

The Depths
And now we arrive at the final encounter, against the Nightmare of Caiatl. Moving down the stairs in front of you will start the fight. The rally flag deposit spot is at the top of these stairs.

The layout of the room is as follows. There are four ledges in this room, two on each side, each with a large relief displaying the symbol associated with that ledge. There are three bells, one on the left, one in the middle, and one on the right. The projections of the Standards required will appear toward the immense bell on the far side of the room, two on each side, next to chains, which will be used in this fight to initiate the damage sequence.

The mechanics of this fight have not changed at all, only this time you will be harangued by the Nightmare of Caiatl and her legions of Cabal. Simply put, you need to identify the Standards needed, eliminate Bellkeepers to make a bell usable, shift realms, kill the Psion on the associated ledge, collect the Standard, kill Bellkeepers and then shift back to the normal realm to deposit the Standards you have. Once 4 Standards have been deposited, the chains next to the deposit points will glow and become vulnerable to damage. Shooting these will ring the immense bell in the background, initiating the damage phase of the fight. Be aware that killing the incorrect Standard Bearer will subtract time from your period spendable in the Nightmare realm, so be careful to only eliminate the ones you need to get Standards from.

Once the immense bell has been rung, you will be dragged into the Nightmare realm alongside the Nightmare of Caiatl, who appears invulnerable. She will then make her way towards one of the bells. If she reaches the bell, she will use this to warp out of the Nightmare realm, ending the damage phase. The only way to do damage to her and stop her is to use the bells yourself. Kill the Bellkeepers for the bell she is heading towards, and then activate the bell with players standing nearby. This will stun Caiatl and provide a damage buff to all players in close proximity to the bell. Hammer Caiatl with all that you've got, then when she unstuns, move to the next bell she heads for and repeat the same process. Once all 3 bells have been exhausted, Caiatl will retreat to the normal realm and take you with her. Repeat the fight as necessary until the Nightmare of Caiatl has been conquered.

Upon her defeat, Eris Morn will warp you back to the Tribute Hall, where you can collect your rewards.

Bosses

 * Nightmare of Gahlran, Sorrow Bearer
 * Nightmare of Emonut, Sworn of Moli Imoli
 * Nightmare of Ka'hok, Sworn of Umun'arath
 * Nightmare of Uroa, Sworn of Shayotet
 * Nightmare of Caiatl, Princess-Imperial

Unique enemies

 * Barrier Colossus (Master mode only)
 * Honored Bellkeeper
 * Standard Bearer
 * Vision of Gahlran

Rewards

 * Armor Sets
 * Deep Explorer (Titan, Warlock, Hunter)


 * Weapons
 * Lingering Dread
 * New Purpose
 * Stormchaser
 * Unforgiven
 * The Epicurean
 * Fixed Odds
 * Heartshadow


 * Equipment
 * Mandate of Strength (Master)

Trivia

 * Duality is the first Dungeon to feature the Cabal.
 * When traveling through Calus's mindscape, the Cabal in the mindscape change. In the normal realm, the Cabal are those from the Loyalists, in the Nightmare realm, the Cabal are those from the Red Legion.

List of appearances

 * Destiny 2
 * Season of the Haunted