Serious Sam 4

Unlocked for beating the level "Anathema under god" for the boss you must shoot the flying fairy guy, then whenever he goes to the pod to heal, just keep spamming it with C4 and then once they retreat from one another shoot the fairy more. Repeat this until the pod is dead and then after this keep shooting the fairy until its dead. To make this easier make sure you have infinite ammo turned on and even tourism difficulty or play on co-op and set respawn timer to 0.

If you do it with those bonuses I did it with just a single minigun and C4 as my secondary so if I tapped LB it would just quickly swap between the only two weapons that I needed. Good luck.