what stage exactly are you at? are you hiding behind the large boxes and the boss is on a higher level?
if so, then:
you need to know that these bosses dye using your infernal shooting, and they are usually in lighted areas where your "mana" drops fast,
here what to do:
1- shoot the lambs at the ceeling, i think they are four,
2- stand up and aim with a "mana" shot (infernal powered shot), from your gun or machine gun and shoot the boss.
3- you may need to do it three or four times, but the idea of shooting the lambs is: hey wont see you easily, you will collect some "mana".
try over and over untill you get it, it is not a bad idea to use some cheat codes, i prefer the infernal +1 trainer and "infinte mana" code.
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