If I undestand correctly, to get "Pacifist", you have to beat both Claws and the Hydra without doing more than 2000 damage on a single attack to anyone. This must also be done on your very first time against it on a particuar file and on Challenging or Heroic difficulty.
I of course, couldn't get it, since I certainly didn't expect to one-shot the upper claw for 16000+ damage and the lower claw for 25000+ damage. First one was with Electric Storm and the second one was with Shock Therapy (Electro Psy build).
romrAremaGeduD: "If I understand correctly, to get "Pacifist", you have to beat both Claws and the Hydra without doing more than 2000 damage on a single attack to anyone." No, to get pacifist achievement you can't deal 2000 damage TOTAL. If you hit 5 attacks of 500 each, you don't get the achievement. I thought what you thought, and went through to get the achievement that way... it didn't work of course, even though I never did over 2000 in a single attack. So I went back and respecced to a total healer build (Hydraulic). It was SOO BORING. I had to just keep healing and healing while my teammates slowly chipped away at the fire claws and hydra. It took like an hour (probably it was literally close to an hour). I couldn't even set both teammates on relentless all the time or my healing wouldn't be enough, so they spent extra moves healing me and each other, especially when killing the 1st claw. In the end I got the achievement.