A stonecharger is a powerstone weapon of mass destruction used by Yawgmoth in the Thran Civil War on Dominaria.
Multiple Stonechargers were based on the Null Moon, an orbital base that functioned as the control center for Halcyon’s constructs. They created a destructive cloud of death. Yawgmoth used one which completely annihilated an army at one point, and several cities were later obliterated, as well. However, the operators of the Null Moon resisted Yawgmoth, and sacrificed themselves to drop their entire payload of Stonechargers on Halcyon. Yawgmoth and his phyrexians escaped to Phyrexia and the fallout of the Stonecharger weapons made them even more horrifying and mutated; the first true Phyrexians.