The Crimson

The Crimson is a biome that may replace the Corruption during world generation. It contains elements very similar to the corruption, but with a red color scheme and bloodier theme. It is also generally different in structure to the Corruption, with less chasms and more web-like caves. Crimson can also spread and "infect" more areas, just like the Corruption and Hallow.

Contents
Instead of Shadow Orbs, the Crimson contains Demon Hearts that may be smashed for loot. Smashing three Demon Hearts will summon the boss, Brain of Cthulhu. Crimson Altars replace Demon Altars and perform the same function. An additional recipe, the Bloody Spine can be crafted from Vertebrae to summon the Brain of Cthulhu.