Mirrodin Besieged, released on February 4, 2011, escalates the conflict between the Mirran resistance and the invading Phyrexians. This set continues the use of Infect, Proliferate, and Metalcraft, while introducing the new mechanics Battle Cry for Mirran forces and Living Weapon for Phyrexian horrors. Players were encouraged to choose a side, reflected in the set’s divided booster packs. Notable cards include Tezzeret, Agent of Bolas, Hero of Bladehold, and Massacre Wurm. With its factional tension and powerful support for artifact strategies, Mirrodin Besieged deepens the war-torn story of the plane.