Master Insurrectionist Achievement
Destroy 25 brain evokers.
To destroy an evoker, you need to use a collector and brass pipes to run steam power to an inhibitor that is placed within about five blocks of the bottom left block of the evoker. The inhibitor will explode, destroying itself, the evoker, and everything nearby. So be sure to stand back when you place the inhibitor (or hook up the last bit of pipe) -- you don't want to get caught in the explosion!
Destroying all evokers on a world will stop brains from randomly spawning on players.