Toxic Sewers

The Toxic Sewers is a second level biome.

The waters of these sewers are contaminated by a poisonous greenish substance that has oozed its way into the pipes. The pipes have decayed and have started rusting and cracking. Boxes of unknown origin litter these filthy tunnels, abandoned to rot. Bars cut off some of the area, with the occasional vocal occupant.

No prisoner has ever reached freedom through these sewers— the toxic atmosphere and revenants make sure of that.

Access and exit
The Vine rune is required to access this biome through the Prisoners' Quarters.

Three exits lead out of the Toxic Sewers: one takes the Beheaded back to the surface atop the Ramparts, the other leads further underground to the Ancient Sewers, and third leads to the Corrupted Prison.

Accessing the entrance to the Ancient Sewers requires the use of a Ram rune, and accessing the entrance to the Corrupted Prison requires the use of the Spider rune. No runes are required to access Ramparts.

Teleportation rune
An Elite Slasher can be found here which drops the Teleportation rune. It disappears after being defeated.

Scrolls
The Toxic Sewers contains 3 scrolls, including 1 Power Scroll and 2 Dual-stat scrolls. Scrolls cannot spawn in areas requiring the Teleport, Ram or Spider runes. On (1+ BSC) there is a bonus Power scroll. When 3 BSC are active, this biome has 2 guaranteed Scroll Fragments, and when 4/5 BSC are active, this biome has 3 guaranteed Scroll Fragments.

Boss Stem Cell rewards

 * 1 BSC: Treasure Chest

Chests and loot

 * There is a 10% chance of a Cursed Chest in the level.

Shops
[needs confirmed data]

Secret areas

 * The blueprint for the Spite mutation can be found in the Collector transition area between the Prisoners' Quarters and the Toxic Sewers.
 * The blueprint for the Frenzy mutation can be found behind the 2 minute timed door in the same transition area.

Enemies
In the Toxic Sewers, you will find plenty of Kamikazes, Disgusting Worms, and Scorpions, which are the iconic enemies of this level. In addition, Zombies, Undead Archers, and Grenadiers dwell here. On higher difficulties, Purulent Zombies, Knife Throwers, and Rampagers make this stage even harder. The Toxic Sewers do not have any unique enemies.

In the table below, you will find which enemies are present in the Toxic Sewers depending on difficulty level. For each enemy, any common, uncommon, rare or legendary blueprints they carry are indicated. When applicable, the minimum difficulty level for blueprint acquisition is specified in brackets.

Conjunctivius lore
Main Article: Conjunctivius

A series of lore rooms scattered around the Toxic Sewers and Ancient Sewers explain how Conjunctivius came to be.

It begins with a nameless, faceless corpse in the Sewers, likely infected by the Malaise. The body is bloated and one of its arms has mutated into a tentacle. Green goo trails from the body towards a small hole in the wall.

After this encounter, the Beheaded finds the same trail of green goo and an empty cocoon next to a bigger hole in the wall, which was made by an adolescent Conjunctivius.

Later, the player stumbles upon the trail of green goo near a corpse. The trail leads to the remains of a huge cocoon and a gigantic hole, carved by the adult Conjunctivius as she escaped.

Finally, a message left by soldiers tells how difficult it was to chain Conjunctivius, likely an order of the King. This explains why Conjunctivius is imprisoned in the Insufferable Crypt when the Beheaded arrives.

Malaise lore
Main article: Malaise The Sewers seem crucial to the spread of the malaise, through its water supply system. For example, piles of contaminated bodies are found rotting in the sewer water. The Beheaded wonders if those bodies are responsible for the initial infection of the citizens, or if those bodies only helped spread the Malaise by contaminating the whole water network.

In a Grimoire within the Sanctuary, the Alchemist writes that people believe the sap flowing through the walls of the Sanctuary is responsible for the Malaise, by contaminating the sewer network. He also suggests that this same substance could be the solution to the epidemic. it is unclear if the substance is in fact the source of the Malaise, or if it's merely a rumor. What is sure is that the Alchemist harvested and used this substance as part of a treatment for the infection, as indicated by the Grimoires of the Ossuary and the Clock Tower.

A giant broken door is found next to a soldier’s note warning not to open this door, lest the rats get out and spread the Malaise. The Beheaded remarks that it is unlikely rats made such a big hole, which implies something else was kept behind the door. It is unclear who or what was behind the giant door. The lack of green goo trail, the fact that Conjunctivius is still in chains when the player reaches the Insufferable Crypt, and this lore room being part of the "Infection" room series and not the "Beholder" (Conjunctivius' old name) series suggest that the creature which escaped was not Conjunctivius. The corpse of Prisoner 236 is found close by; he presumably died while trying to escape.

Alchemist Grimoires
Main Article: The Alchemist

In the Sewers and the Ancient Sewers, the Alchemist collected mold and mushroom samples for his experiments. However, the growing numbers of revenants made his work increasingly difficult."It is becoming increasingly difficult to collect mold samples in these sewers. There are too many revenants."

"Gollum" and the Teleportation Rune
Main Article: Gollum

When the Beheaded first enters the Toxic Sewers, he meets an unnamed character (called "Gollum" in the game files, a reference to The Lord of the Rings) stuck behind bars who asks him to fetch "his" rune — heavily implying it does not truly belong to him.

When the player kills the Elite Slasher who holds the rune, he later encounters the mysterious character again but refuses to return the rune. "Gollum" then warns the Beheaded will regret this and swears he will eventually get his rune "back".

A lore room full of teleportation coffins can be found with his crushed corpse, putting a sad end to this story.

Due to a bug, the room continues to spawn in the biome even in future runs, regardless of the player obtaining the rune or not.