The Underground Crimson is a Hardmode biome, being one of the biomes that spawns when the Wall of Flesh is defeated. It is the underground version of the surface-level Crimson, and appears at and below the cavern layer. It operates similarly to surface Hardmode Crimson, being comprised of Crimstone and Crimsand, though it spawns different enemies. Underground Crimson spreads just like surface Crimson, and similarly can not spread to The Hallow (nor to Underground Hallow). Additionally, small pockets of Underground Crimson can be created through the breaking of Crimson Altars, which can convert a single random stone block in the world into Crimstone upon their destruction.
A player is considered to be in an Underground Crimson biome when there are at least 200 crimstone/crimsand blocks near the player.
Note: Most characteristics of surface Crimson apply to the Underground Crimson, with the exception of the enemies that spawn. See Crimson for more extensive information.
This content is transcluded from Biome backgrounds § Underground Crimson.
On the Desktop version, Console version, and Mobile version, the following backgrounds are used. On the Old-gen console version and version, the cavern layer background for any other biome the player is in is dynamically tinted red.
[Crimson Ice] Bumpy red ice wall with Blood Jellies and eyeballs frozen within it
- Desktop 184.108.40.206: Added Otherworldy Underground Crimson track from the cancelled Terraria: Otherworld.
- Desktop 1.2.4: Now has its own specific theme music.
- Desktop 1.2.3: Added biome specific stalactite variations.
- Desktop 1.2: Introduced.
- Console 1.02: Introduced.
- Switch 1.0.711.6: Introduced.
- Mobile 1.2.6508: Introduced.
- 3DS-Release: Introduced.