Defeating Plantera for the first time reduces the speed of the Crimson's spread by 50*1/2 (50%).
While its spreading capabilities are very limited during pre-Hardmode, it spreads much faster and more aggressively after defeating the Wall of Flesh. This means that it slowly converts certain susceptible tiles that are in the vicinity of existing Crimson blocks. The Crimson spreads itself, similar to the Corruption and the Hallow. Thorny bushes will begin to sprout on the grass and will damage the player when touched. For an area to be considered a Crimson biome, at least 300 / 200 tiles of Crimson grass or Crimson blocks must be present. If enough Crimson manages to take over a new area, then that area will eventually adopt the Crimson's theme music, background, and water color. Chasms, Crimson Altars, and Crimson Hearts will only appear upon world generation, and will not spawn in a Crimson area that has formed through spreading. The Crimson spreads, meaning it slowly converts adjacent tiles to their Crimson variants. Chasms consist of Crimstone, which can be blown up by explosives, mined with a Nightmare/ Deathbringer Pickaxe or higher, or purified to Stone by using Purification Powder. Crimson Altars generally line the chasm's passages, appearing inside and around it. Every chasm has an entrance on the surface and leads to a large, circular cavity, then branches off into small "fingers" which end with a Crimson Heart. The Crimson contains multiple chasms, extensions of the biome into the underground.
Crimson enemies tend to have slightly higher stats, such as health, defense, and damage. The tools, weapons, and armor obtained via Crimson material generally have minor advantages over those obtained via Corruption materials however, Corruption tools are slightly faster. Both contain similar hazards and feature their own unique enemies, items, and blocks. Every world will contain one of the two generated randomly except for special seeds (each with a 50% chance of occurring) or chosen by the player upon world creation ( only after the Wall of Flesh has been defeated in any world). The Crimson is an evil biome with a fleshy infection, red gore theme, in contrast to the dark purple wasteland theme of its counterpart, the Corruption.