At a glance, the battle leaned for Warchief Might's side. However, Warchief Might and Lotord know it is the opposite. None of their attacks manage to truly hurt him. They could only fight with this absurd monster for long because of his injured arm.
After he cuts his own arm, the monster is adamant about healing his arm rather than focusing on fighting them. Although the healing and regenerating power is not using his own mana or miasma, he still needs to put much effort into controlling divine energy.
This slight distraction makes him unable to fight properly against Lotord's attack. Both Warchief Might and Lotord also notice this situation. They didn't know why the monster was adamant about fixing his arm. Still, they decided to take advantage of this situation.