Originally Posted by
Magpai
No, this will guarantee a fail. When the arms die, they deal damage to the body equal to their own maximum health (I believe it's 15%). You need to get the torso's health between X and 2X, where X is the max health of an arm. Destroy both arms at about the same time and the boss will keel over dead without any further damage. If his health gets below X then the first arm that's destroyed will kill him as well, before the other arm can die, and you'll miss it.
If the FIRST arm you kill kills the body then you won't get it. If you kill one arm, then the other and the second kills him, that's fine.