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Nightmare Containment is a six-player public event/seasonal activity for Season of the Haunted located within the Castellum of the now derelict Leviathan. It has the unique function of being able to be accessed like a normal public event, or through matchmaking.
In order to suppress the surge of Nightmares and perform a ritual to sever Calus's connection to the Lunar Pyramid, Eris Morn sends in the Guardians on a mission to harvest the essence of Nightmares on the Leviathan, destroying them and binding them to the Crown of Sorrow, using the Nightmare Harvester. Doing each of the Nightmare Containments allows Eris the time and power she requires for her Severance Ritual.
Nightmare Containment is a horde-defense game mode in which the players must defend the Nightmare Harvester from waves of Scorn and Cabal enemies. The event takes place in three of four areas of The Castellum, each corresponding to an entrance to a part of the ship. The event will begin in front of either Royal Pools, Pleasure Gardens, or The Gauntlet and will make their way to one of the other two locations, progressively getting more difficult, before ending in a boss battle that always takes place in front of the entrance to Emperor Calus's Throne Room. Each Nightmare Containment consists of three tiers with four phases each.
The event begins when a play places a Nightmare Harvester on the designated location. There will also be a place to plant a Rally Banner nearby when first starting the activity. During this phase, players are tasked with binding Shards of Dread by killing combatants and depositing Cores of Dread into the Nightmare Harvester. Scorn will constantly spawn in order to impede progress and swarm the Harvester. Two Ultra Scorn Chieftains or Raiders named Dread Bearers will also spawn. Killing these Dread Bearers will drop Cores of Dread, which when deposited, will give a large amount of Shards of Dread, but also spawn an Overload Chieftain, with a small group of Scorn, that will close in to the Harvester, stealing Shards of Dread if it gets in contact with it. Every so often, the Harvester will also produce a Scythe Relic which can be used to deal with the enemies. Once the Harvester has enough Shards, this phase will end.
The second phase begins when Calus attempts to impede player progress by summoning a large amount of Cabal close by. During this phase, no Scorn will spawn. Players must kill Major Psions named Egregore Atavists, which are protected by Atavist Illusions. When the Illusions are defeated, the Atavists will spawn in with a psionic shield around them that blocks incoming damage, forcing players to walk into their bubble to kill them. Once all the Atavists are dead, the second phase will end.
The third phase is a repeat of the first, but even more enemies will spawn, alongside two extra Dread Bearers. After the Harvester has had enough Shards, the fourth phase will begin. Calus will summon a powerful Cabal boss,Valus Thu'ur, Vessel of Nightmares, a Colossus. When the boss reaches half health, it will pull up an immunity shield that can be deactivated by destroying Resonant Splinters. After this boss has been defeated, the event will move onto the next tier and a box of ammo that refills Heavy and Special ammo will appear.
Tier Two is mechanically the same as Tier One with a few notable differences.
Tier Three is the final boss of Nightmare containment. The boss and mechanics rotate on a weekly basis. Throughout all three, constant waves of Scorn or Loyalists will be spawning to impede player progress.
Nightmare of Elykris, the Machinist is a large Scorn enemy. After dealing one third of its health, Elykris will pull up an immunity shield and six resonant splinters will spawn around her. Once all are destroyed, two Abominations named Emissary of Elykris will spawn beside it. Killing these two Abominations takes down its shield. This mechanic repeats once more after the next third of its health is dealt.
Nightmare of Anaphex, Sworn to Otzot is a Psion Flayer. Periodically, Anaphex will unleash a weave of psonic energy which traps players in a cage. In order to escape, players can shoot one of the circles that make up the cage. If a player is not freed in time, they die. When Anaphex's health is reduced by a third, it will disappear and three Atavist Illusions will spawn. Killing these will spawn an Egregore Atavist in its place. Killing them all causes Anaphex to reappear. This mechanic repeats once more after the next third of its health is dealt.
Nightmare of Navôta, Eir-Spawn is a large Hive Wizard . After dealing one third of its health, Navota will become immune and summon two Dread Bearer Raiders. Killing them and depositing their Cores of Dread will bring down her shield. This mechanic repeats once more after the next third of its health is dealt.
The chest at the end of Nightmare Containment will only drop world drops. You can obtain Season of the Haunted Weaponry by binding Vestiges of Dread, which will also give you a Bound Presence, which are needed to gain better loot in the Sever missions.