Currently I feel as though superbolide is the only invulnerability that can be used without healer assistance. My suggestion is to change superbolide to instead make it so for 10s your hp cannot change and during that time have a percent of the damage you take be stored up and heal you at the end of the duration similar to macrocosmos on astro. This way GNB can better use their invul as regular mitigation much like how the other tanks are capable of doing and this would solve the interaction of GNB dying while using superbolide do to the current order of operations being, set hp to 1>become invulnerable making is possible but not common to take damage after setting hp to 1 and before you become invulnerable.