The fourth mutation of the creature known as G, formally
William Birkin.
A major shift in the creatures form occurs here when its arms turn into legs as the creature gets down onto its stomach, and a mesh of razor-sharp spikes emerge upwards from its chest to form a circular mouth. It's at this point it becomes incredibly quick and difficult to target, so take careful aim. It has a habit of jumping down on you from above, so keep on the move to avoid being surprised by this attack.
Don't get too close as with these four limbs it will easily pummel you repeatedly with very little room for escape. Use your biggest most powerful weapons for this battle.