My main is my ik barb and his merc doesn't have any special gear just rocks a regular reapers toll crown of thieves and a duri shell, I wouldn't say I'm tearing it up in inferno, but my merc hardly ever dies and the holy freeze+decrep are huge! I am able to slowly but surely work my way through the mayhem. eventually I'd like to make him a focus for the aura and hopefully find a decent eth reaper and eth fortitude