Downpour

Downpour is the first new environment added in Repentance. The theme of Downpour are flooded, haunted storm drains with many supernatural enemies and elements. Though there is some overlap with the due to both featuring water flooding, the Flooded Caves' unique enemies are almost exclusively 'drowned' or 'bloated' as opposed to Downpour's more haunted theme.

Treasure rooms in Downpour always have two items to choose from. One of the items will always be unknown, however this can be circumvented with the.

After is unlocked, a locked door to Downpour I or II will appear upon completing // I or II, respectively. The locked door requires a key to enter.

Flooding & Storm
Downpour features a heavy emphasis on water and flooding. The entire floor is submerged in a pool of waist-deep water, that some enemies such as Small Leeches and Striders are capable of using to swim over pits. Numerous Deep Gapers also hide beneath the water and emerged when all enemies in the room have been killed. The reflection visible in the water is also utilized by Wraiths, which they are always visible in even though they are invisible otherwise. There is also a storm playing out in the background, which when lightning strikes, brightens up the room and reveals any Wraiths in the room.

Monsters

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Knife Piece
Downpour II (or II) contains a special area in which Isaac can acquire the, one of the key items for accessing. Two unique features can be found here:
 * A White Fire Place that cannot be extinguished, touching which separates Isaac's body and soul, converting Isaac into  for a brief time. Clearing any room will return Isaac to normal.
 * The Lost will hold the if it is unlocked as a starting item. (Beware: the Holy Mantle will not be active until Isaac leaves the room. Taking damage in the same room after touching the white fireplace will be fatal.)
 * A 1x1 room with a mirror on the icon. There is always a mirror that can't be accessed normally.

The mirror can only be entered as the Lost (or ), after which it leads Isaac to the Mirrored world, where he can find.
 * All rooms will be generated without any items or pickups. However, any means of creating items or pickups after room generation (including normal room clear rewards, destroying props, beggar payouts, and the boss room item) will still work.

Once Isaac has cleared one room, has obtained the Knife Piece, and returns through the mirror back to the real world, he will be converted back to the original character. To acquire and complete the process, be sure to head to / II next.

Trivia

 * Downpour is referred to on Isaac's Last Will as "Some Sewer".
 * Antibirth used to have different method of unlocking first Knife Piece. Somewhere on the floor, there was a seemingly empty dead-end room with a minimap icon that indicated the room had a chest. Bombing the center of the room would open a hidden stone chest containing Knife Piece 1.
 * In Antibirth, The Haunt could spawn as a boss.
 * There's a level called Downpour in Super Meat Boy, another of Edmund McMillen's games.
 * Gapers and Frowning Gapers are tinted blue if encountered.
 * As well, Clottys that spawn in the floor will appear wet and shiny.