Bloody Spine

Crimson only, and it ignores the clock, which makes the Brain the most schedulable of the early bosses. Dig out a flat pocket in the crimson underground before you throw one, because fighting it inside the natural chasms is miserable: the walls eat your shots and the swarm of creepers uses the tunnels better than you do.

The fight can be held in a corruption world, but everything has to be imported. That world grows neither the crimson blocks the summon needs to register a biome nor the materials the item is made from, so it means hauling both in from another save. People do it to finish an item list. It is not worth the trouble on a normal run.