The achievement is pretty self explanatory that you need to win a match with all of your friends downed. All you need to know is that it has to be the new guy (your main character) that has to be the last man standing. You need to be at the point in the game where you have 3 friends with you in the fight. The best tactic I found is to beat all of your opponents except one and weaken the last person to be a one hit kill, now keep the new guy at the back of the map and keep skipping turns until all of your friends have been downed then defeat the last opponents the achievement will pop.
If you would like a video guide I will leave mine below.