Crimgrass

Grass or weeds that have been affected by The Crimson. What used to be normal grass is now the color of bloody exposed organs and bearing sharp spikes as long as a human finger, crimgrass randomly produces crimthorn from any of the seed-bearing grass in its patch.
A sample of crimstone was brought to the unnamed robot's Sphere, and it was left with its other supplies on top of a Grass Block. One of the Grass Blocks was converted to a Crimgrass Block, which spread from there.