Lord Benedict hint? Combat hint?

[Doom]

I'm trying to figure out this game, but struggling hard. I'm level 3, have the best armor I can find, 3 pieces of Rusty gear...and I'm hopeless in combat.

I'm currently trying to beat Lord Benedict, who is allegedly level 3 (but has lots of HP). I was hoping that with a ton of healing potions I could do it...but nope, can't drink those by the gallon. I was hoping I could lure him into a trap...but nope, he's immune. I was hoping some prep potions would help, but armor potions an dodge potions still don't make any difference.

Is there a special trick to beating him that I just missed?