At level 12 with unarmed, I defeated the Master fairly easily just by punching his eyes, like some eye-hating maniac. Fortunately, a lot of the Super Mutants that came in behind me would kill each other by missing me and hitting each other.
Lou (that's the lieutenant mutant, right?) was a lot harder simply because he seemed to always get critical hits that did at least 200 damage. At first I thought it was a scripted fight that you had to lose. I kept trying, though, and eventually he'd do small enough damage for me to survive (I think my HP was around 110) and I managed to defeat him, though I was constantly scared of another ridiculous crit.
Lou (that's the lieutenant mutant, right?) was a lot harder simply because he seemed to always get critical hits that did at least 200 damage. At first I thought it was a scripted fight that you had to lose. I kept trying, though, and eventually he'd do small enough damage for me to survive (I think my HP was around 110) and I managed to defeat him, though I was constantly scared of another ridiculous crit.