Evil biomes



An evil biome is a naturally spreading, hazardous biome that has generally negative effects on entities inside or around it. The two evil biomes are The Corruption and The Crimson, only one of which will always spawn in a world. Upon world creation, there is a chance for either one to generate. On the, a player can choose whether they want Corruption or Crimson to generate in their world or they can leave it to be determined randomly. On the, the player only has this choice if Hardmode has been entered in at least one world.

Corruption or Crimson is saved as the world's naturally generated evil biome, and determines:
 * whether Shadow Orbs or Crimson Hearts are generated;
 * whether Demon Altars or Crimson Altars are generated;
 * whether a Corruption Chest or Crimson Chest is generated in the Dungeon;
 * whether Underground Corruption or Underground Crimson is created when the Wall of Flesh is defeated;
 * whether Corruption- or Crimson-related blocks are seeded as Altars are smashed in Hardmode;
 * whether some NPCs will sell Corruption- or Crimson-related items during a Blood Moon or Solar Eclipse; and
 * which Biome Mimic is spawned when a Key of Night is placed in a chest.

It is possible to create an artificial Corruption/Crimson, seeding an area with the opposite evil biome. While this is traditionally done with materials brought over from another world, there is another option on the : If the Dryad is housed in a Graveyard during Hardmode, she will sell grass seeds from the other evil biome's. This allows, for instance, obtaining the Biome Key /  of the opposite evil biome, as that is dependent on the biome the enemy is killed in, regardless of whether it is a "natural" biome or "artificial" biome. This will not however provide a Dungeon chest to go with the key.

The evil biome is predominately comprised of chasms made from infected stone (Ebonstone or Crimstone). However, the biome can overlap other biomes, providing corrupted versions of the Forest, Desert, Snow, Jungle, or Ocean biomes. This can be evidenced by the presence of purple/red grass and Ebonwood/Shadewood trees, purple/red Cacti and Ebonsand/Crimsand, Purple Ice/Red Ice, or purple/red Palm Trees. Infected Jungle areas turn into corrupted Forest (with the Mud Blocks converted to Dirt Blocks).

While in pre-Hardmode, the only biome capable of spreading the evil biomes is infected surface Forest, via infected grassy blocks (see below for details).

Corruption and Crimson counterparts
Certain items are exclusive to either The Corruption or to The Crimson.

The following items are considered counterparts to each other. It should be noted that counterparts do not necessarily share the same stats or behaviors.

The Corruption
The Corruption presents a purple "corrupted" theme, with purple grass, trees and stone. Thorny Bushes and unique enemies (beginning with Eaters of Souls and Devourers) make the area dangerous and potentially deadly for newer players. The Eater of Worlds can only be summoned in the corruption. The Corruption contains deep vertical chasms (which can easily result in death from fall damage), with cross tunnels well below ground. Shadow Orbs appear deep underground, usually at or near the bottom of chasms. Destroying a world's first Shadow Orb will always drop a Musket and some Musket Balls, which automatically fulfills the criteria for the Arms Dealer to arrive. Destroying three Shadow Orbs will result in the spawning of the Eater of Worlds.

The Crimson
In contrast to the Corruption, the Crimson presents more of a red, gory theme, with red grass, stone, and foliage. Unique enemies that only appear in a Crimson world include Blood Crawlers, Face Monsters and Crimeras. The Brain of Cthulhu, the alternative to the Eater of Worlds, can only be summoned in the Crimson. Crimson-infected stone is called Crimstone, and like its Corruption counterpart, can only be mined with a Nightmare Pickaxe/Deathbringer Pickaxe or better. Like the Corruption, the Crimson contains deep chasms, but these are differently shaped: A winding tunnel from the surface leads to a large cavern, with secondary tunnels spreading downward from the cavern. These tunnels look quite like hands. While long falls are less of a hazard here, the area is still quite dangerous. Instead of Shadow Orbs, the Crimson contains Crimson Hearts, placed at or beyond the end of the secondary tunnels. Destroying a world's first Crimson Heart will drop The Undertaker with some Musket Balls, which, like their Corruption counterparts will fulfill the criteria for the Arms Dealer to arrive. Destroying three Crimson Hearts will result in the spawning of the Brain of Cthulhu.

Spread
Both the Corruption and the Crimson will spread themselves, similar to the Hallow. This means that they slowly convert certain susceptible tiles that are in the vicinity of existing Corrupt/Crimson blocks. While their spreading capabilities are very limited during pre-Hardmode, they spread much faster and more aggressively after defeating the Wall of Flesh. Defeating Plantera for the first time reduces the overall spread speed of all three biomes by.

Corrupted and Crimson Deserts
The evil biomes can overlap deserts, and in Hardmode, can spread through them, creating Corrupted and Crimson deserts. In the Corruption, sand is replaced with Ebonsand, and in the Crimson, sand is replaced with Crimsand. Unique enemies not found in the normal Corruption and Crimson can be found in the biome's desert variant.

Purification
In Hardmode, the Corruption or Crimson (like the Hallow) can spread out of control; without player efforts, the evil biome and Hallow will together take over the entire world.

In pre-Hardmode, players can use Purification Powder to purify small portions of the Corruption/Crimson, and Sunflowers to block spread of infected grass. However, it is not until Hardmode that the spreading biomes become a major issue.

In Hardmode, a good strategy is to dig 3-tile-wide tunnels around the Corruption/Crimson, containing it. However, near the surface Thorny Bushes can spread the Corruption up to 6 tiles, so the tunnels there need to be 6 tiles wide or lined with non-corruptible blocks.

Removing the Corruption or Crimson wholesale, or reversing its spread in Hardmode, effectively requires the Clentaminator. This can be purchased for from the Steampunker, who arrives after at least one mechanical boss has been defeated. Using the Clentaminator with Green Solution (also purchased from the Steampunker) can purify large sections of the evil biomes. However, most players will want to keep some well-contained pockets of the biome, as the enemies there have unique drops (some of which are recommended to advance in the game).

The evil biomes are also blocked by the presence of the Hallow, and vice versa; even before obtaining the Clentaminator, seeding the Hallow is an alternate strategy to limit the spread of Corruption or Crimson. However, this may mean eventually having to deal with an out of control Hallow in the future.

Tips

 * On the versions, one-half of the world generation progress bar will be green, and the other half purple or red, depending on if the world is to have Corruption or Crimson. The step in world generation in which the Corruption is created is called "", and the step in world generation in which the Crimson is created is called "". Also, a tree at the side of the world name in world selection has one green/normal side, the other purple/red (indicating Corruption/Crimson respectively). In Hardmode, part of the tree will be yellow, representing The Hallow.

Trivia

 * A always contains both evil biomes.