It's not really god mode. It is a “miss” mode. The enemy “misses” the direct hit on your team. Unfortunately, there is so much splash damage and other types of damage etc. that you take, which is why you can easily lose if the opponent is too strong. I got to 12th rank. The fights last forever because the opponent has golden heroes who, with every attack, buff the entire group with higher HP and damage than I can do. I only manage to defeat the opponent with Regina (Immunity) and her multi-attack after many rounds of stacking if I use Rachie's "Suppresses" after rounds 15-20 to reset the enemy units.
