The Blackstone Arm is a heavy weapon which grants slowness when carried in hand but can has the power of the Blackstone Golem in it and can throw blackstone blocks. It has to get charged by holding right click and is made out of blackstone and the blackstone heart.
Hold right click for 1.5 seconds to charge it, indicated by a red glow on the arm. By releasing right click, a blackstone block will get throwed.
When the player has the blackstoned effect, there is a hidden secret when throwing blocks with the arm.