A immunity shield is unrealistic. If the saber shank started to become overcharged with lightning to the point where all bullets deflected off of it THAT would be cool AND make sense. Imagine seeing that giant shank pulsing in lightning, a little lightning storm above it, and lightning going from the shank to the ground around it COOOOL! If Sepiks paused and started to channel some Siva Energy and you had to hit one of the many weak points on him that did bonus damage to make him stop that would be AMAZING!! Point being, immunity phases are FINE. But make them realistic, don’t just give the boss a white shield. Spice it up!