Lawbringer is AWESOME that's why Babyhell thinks its cheating. Other than for the undead just don't expect it to kill very quickly. I just finished a Wolfbarb using an Act 5 merc armed with a Lawbringer. It says it has a 20% chance to cast Decrepify, but I felt it was less often than 20%. Of course the duration is 3 times as long as Reaper's so you don't need it going off as often. I'm guesing that part of the reason I felt the decrepify wasn't hitting the 20% mark was the merc also using stun.
The knockback for Sanctuary is also very helpful in more places than Act 2. You need to realize that the knockback is from the merc and not your character. Depending on positioning this means that the knockback could actually knock the monster into you rather than away from you.
Back in the day I had a Charger that used an A1 Merc with Giant Skull / Treachery / Wrath that was similar in that she had decrepify and knockback. She was very effective, and nice for spreading out monsters so my charger could pinball off them. I have to admit, the A5 mercs have been tempting me this time through, and I've never done one with Lawbringer. If another Lem drops, I may give that a try.
Update: 100 Pit Runs Complete
I arbitrarily decided I'd do 100 pit runs, see what dropped, then move on. I ended up using the rare BA I picked up along the way. It upped my top-end damage from ~2800 to ~3600 and AR from 5900 to 7000. It felt a little faster kill-wise, and my only complaint was I'd forgotten how low the durability on Berserker Axes was.
Rest of gear: Smoke / Vamp Gaze / Cat's Eye / Rhyme / Dwarf Star / Manald Heal / LoH / War Travs
Merc: Tal Rasha's Helm / Insight GPA / Treachery
I just focused on kill speed instead of loading up on MF because I wanted to find some bases for runewords, especially my weapon.
Finds
Runes - Gul, Ko, Fal
RW Bases - 4os Eth Balrog Blade, 3os PB for Crescent moon and 5os PB for Grief. Some elite armors with sockets as well.
Magic items - Sparkly chest dropped an Oculus. Natalya's Mark.
No base for Oath, sadly. Though an Eth Berserker Axe was ideal, I would have taken an Eth Ettin Axe, Small Crescent, or Cryptic Sword. No luck, even with using cube socket recipes, and I'd have taken a 0os Small Crescent to Larzuk. I was tempted to go 2-handed with the Balrog Blade, but decided I'll just head on to LK and see if I can get a Lo rune to drop on the way.
I may go back to the Pits loaded up with MF gear at some point, but for now it's on to Lower Kurast!
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