The Corruption



The Corruption is a biome characterized by purple "corrupted" Grass and Trees, and hazards like Eater of Souls, Devourers, and Thorny Bush growth. New players will want to avoid The Corruption prior to acquiring better equipment (generally Silver or Gold Armor, Weapons and Tools). Corruption features a dark background with limited daylight, and unique theme music.

The Corruption area that generates initially with the World is home to Chasms that lead to Shadow Orbs and Demon Altars. Chasms represent an additional hazard to players due to Fall Damage, and players without a climbing aide like the Grappling Hook will have a tough or impossible time climbing out of them, should they survive the fall. Chasms are lined with Ebonstone, which can only be mined with a Nightmare Pickaxe or higher. Corruption can also spread to areas not initially infected, and can be seeded by the player in new locations using Corrupt Seeds. Chasms, Shadow Orbs, and Demon Altars will not spawn in Corruption that has formed this way. Corruption enemies like the Eater of Souls, as well as Thorny Bushes, will spawn in spread or seeded Corruption. If enough Corruption takes hold in a new area, it will begin to feature the Corruption theme music and background.

Purification Powder can be used on corrupted blocks to turn them into their regular counterparts. "Purified" blocks can still become Corrupted again afterwards.

Sometimes, there may be Crimson biome in a world instead of Corruption.

Spread
In normal mode (pre-Hardmode worlds), corruption can spread, but only under limited conditions:
 * Corrupt grass can spread in a manner similar to normal grass, converting adjacent Dirt tiles with at least one side open to air (only in the Surface Layer).
 * Corrupt grass can also displace normal and hallow grass, unless the grass has a Sunflower planted on it.
 * Corrupt grass may sprout Thorny Bushes, which can spread corrupt grass according to the same rules.

Naturally-occurring corruption will often be halted by various natural barriers (stone, desert, etc.) before it is even discovered, but care should be taken when creating an artificial corruption biome that it does not spread further than intended.

Hardmode
Once the Wall of Flesh is defeated, a world enters Hardmode. New areas of Corruption and Hallow are immediately created that extend from the Underworld up to the Surface, sometimes intersecting existing Corruption. Corruption begins spawning more dangerous enemies, such as the Corruptor, and underground, the Clinger.

Corruption spreads much more aggressively once the world is in hardmode:
 * In addition to corrupt grass, thorns and plants, also ebonstone, ebonsand, purple ice and red stucco generate corruption.
 * Grass can still be converted to corrupt grass, and corrupt grass can cover new dirt as in regular mode.
 * Mud can now be converted into dirt.
 * Jungle grass can also be converted into corrupt grass (changing the underlying block type to dirt).
 * Stone can be converted to ebonstone.
 * Sand can be converted to ebonsand.
 * Ice can be converted to Purple Ice.
 * Sunflowers no longer block the corruption, and will be uprooted if the grass they are planted in is corrupted.
 * Corrupt grass is still limited to the Surface Layer, but ebonstone and ebonsand can spread through any depth.
 * Blocks that are up to three squares away from an existing corrupt block can be converted (even if uncorruptible blocks are in the way).

Corruption does not spread through other materials, even natural materials like clay and snow. Silt can be converted as part of the initial burst when you first defeat the Wall of Flesh, but not at other times.

In order to stop the spread of Corruption in Hardmode, the player must create a gap of at least three tiles containing empty space or non-corruptible blocks. Hallow blocks will also stop the spread of Corruption, but will spawn its own hazards as well.

Corrupted Desert
In Hardmode, Corruption spreads through Deserts, transforming it into Corrupted Desert. It is very similar to The Corruption: The theme music is the same, and enemies are the same, with the addition of Dark Mummies.

Sand is replaced by Ebonsand. Although their color is different, cacti still drop ordinary cactus when cut. Waterleaf is not able to grow in corrupted deserts.

History

 * Killing a hardmode boss reverts the spread back to normal mode speed.
 * Bug: Red stucco spreads corruption, probably a typo and ebonstone brick was supposed to spread instead.