The Darkness

The Darkness is a secret world that the player may not encounter in most runs. The only way to access it is by killing 3 Friendly Droids that spawn in a special room. This will cause the message "Wrath takes hold." to appear, and the next world will be replaced by the Darkness.

All enemies that spawn here are world-exclusive to the Darkness, although The Shadow may be seen in other worlds through random buttons.

Environment
The Darkness takes the environment of the world it replaces. Environmental Hazards of the replaced world are also changed.

Other then that, the darkness also changes the walls to black, the floor to grey, and the time to night.

Rune
This special object is completely exclusive to The Darkness only. Runes will rapidly spawn multiple The Corrupteds and The Phantoms with only 1 HP, then disappears afterwards.

Trivia

 * The Darkness is one of three worlds that disables warping, if you try, a text will pop up saying "You cannot escape."
 * The Darkness and Blood Moon are the only worlds whose time can't be set to day. Trying to do so will have text pop up saying "It's too dark."
 * It is possible to skip the boss fight by using a Skipping Stone. The Dark One also dies instantly to Flashlight.