Forgotten Sepulcher

The Forgotten Sepulcher is a fifth level biome. According to the loading screen quotes, it was once a tomb for important officials and nobles but was abandoned after the Malaise epidemic. The burial rites included killing the delegations of the entombed dignitaries and using their bones to decorate the walls.

Access and exit
The Teleportation Rune is required to access the Forgotten Sepulcher from the Stilt Village. There are also entrances from the Slumbering Sanctuary and the Graveyard.

The biome exits to the Clock Room. After beating the Giant once and with two or more Boss Stem Cells active, the Beheaded can also exit to the Guardian's Haven through a door near the Clock Room exit.

The Darkness
The Darkness is a mechanic found only in the Forgotten Sepulcher, unless the Custom Mode gameplay modifier Follow the Light is enabled. The level appears dark except for permanent and temporary light sources, which illuminate small areas around them. The temporary sources are activated when the Beheaded touches them and burn out after a while.

If the Beheaded has been away from the light for 12 seconds, the Darkness begins to eat away at its health. The damage gradually increases from 0.1 to 6 per tick, with ticks every 0.3 seconds. Going near a light stops the damage and resets the 12-second timer and damage per tick. Killing an enemy reduces the Darkness by 11%.

Darkness damage does not trigger death by curse, and the mutation Disengagement does not protect from it.

Explorer's Rune
A room with two elite Dark Trackers can be found at the end of the biome. Defeating those elites gives you two Crypt keys, which are required to proceed to the room beyond two elite room, which contains the Explorer's Rune. Those rooms stop appearing after obtaining the rune.

Scrolls
The Forgotten Sepulcher contains 3 Power scrolls (with a fourth located in a cursed chest on 3 BSC), and 2 Dual-Stat scrolls. When 3 Boss Stem Cells are active, this biome has 3 guaranteed Scroll Fragments, and when 4/5 Boss Stem Cells are active, this biome has 4 guaranteed Scroll Fragments. These can spawn in areas requiring the Teleportation Rune, but not the Spider Rune.

Boss Stem Cells rewards

 * 1 BSC: Treasure chest
 * 2 BSC: Exit to Guardian's Haven, 2-choice item altar
 * 3 BSC: Cursed chest
 * 4 BSC: 2-choice item altar

Chests and loot

 * Two guaranteed cursed chests are found behind 1 and 3 BSC doors

Shops
[needs confirmed data]

Secret areas
The blueprint for the Hayabusa Boots is found in a secret area behind a locked door near the Clock Room exit. To reach it, the Beheaded must defeat two Elite Dark Trackers. These two Elites will always be present, and the blueprint will be replaced by a gem or item on subsequent visits.

Blueprints from enemies
The blueprints for the Spiked Shield and Death Orb are exclusively found in this biome and are looted from Cleavers.

Enemies
Dark Trackers and Cleavers could be considered iconic of the Forgotten Sepulcher, particularly because Cleavers are unique to this biome. In addition, Shockers, Kamikaze, Inquisitors and Lacerators can be found, as well as Knife Throwers, Shieldbearers, and Failed Experiments on higher difficulties.

The table below lists which enemies are present in the Forgotten Sepulcher on each difficulty level and which blueprints each may drop. When applicable, the minimum difficulty level for blueprint acquisition is specified.

Alchemist Grimoires
Main Article: The Alchemist

The Alchemist was researching the Malaise in the Forgotten Sepulcher, but the bodies kept waking up. In addition, the Darkness was making his work difficult. This prompted him to leave the area.

Other lore rooms
Nathan Drake, the protagonist of the Uncharted series, is found dead in a pit. He was looting sarcophagi but never managed to get back up because his rope was too short.

Loading screen quotes

 * "High-ranking dignitaries were embalmed in sarcophagi. After a somewhat brutal ceremony, the skulls of their delegation were used to decorate the walls of the chamber."
 * "Once reserved for high-ranking dignitaries, the sepulcher became a tortuous labyrinth, its reaches fading into obscurity and myth..."
 * "To get out alive, simply follow the light. No, not that one, the other... Yes, there, the... No, uh... Wait a minute, where are we?"