Allow Soloman Grundy to resurrect at least 30 of Ra's al Ghul's defeated guards before defeating him. To get the lazarus factory feat the tank needs to pull soloman grundy onto the dead GUARDS until he smashes a barrel on the ground to ressurect them. There are groups of dead GUARDS scattered throughout the arena. Have the tank pull grundy around in a rotation. It helps if the entire group is near the tank so that when grundy does a jump attack he jumps directly on the dead GUARDS. It can be hard to count exactly 30 while everything is going on so I recommend you keep going around until you feel certain you have resurrected 30 guards.
