Situation: 3 friends and I play 2 nights in a row for this achievement. We finally get our strategy down pat. we play through no mercy, no one takes any damage (though a hunter does pounce one of us for 0 damage 1 time) and we get on the chopper. no achievement for any of us. We all knew how much damage we took prior to starting the finale, so we watch the end credits, no extra damage.
So, even if its on easy, does a pounce for 0 damage or even 1 friendly fire shot (on easy it causes no damage) ruin the cheevo?
Edit: I'm off to bed. I'll look in this thread in the morning. Hopefully you guys here on EB can give me the low down.