This one of the more challenging ones. You have to save the exact number of civilians without them dying. You and your team have to work together to defeat all enemies before making the civilian follow you. Don't rush on this challenge, enemies tend to spawn once you have the civilian following you. Just tell the civilian to wait in a safe area while you take out the remaining enemies.
*You can create a match with just 2 people to start, you can choose up to 4 players.
Note: Must complete all challenges under the given time, and with the exact amount goals to receive the achievement for the given challenge!