This achievement is fairly time consuming and requires some patience.Requirements: 2-4 People*
*It can be boosted with a total of 2 people, however for the sake of co-op, it's best to get 4 people together.Small/Large Team
All parties must search for Small/Large Team matches at the same time to get paired together. Take turns winning 10 of each game type (Small & Large). If you boost in ranked matches, you can also work towards the 500 kills achievement.For Small Team matches:
Usually end up being Team Deathmatch matches, where players can take turns getting their 500 kills (40 kills/match).For Large Team matches:
Try to get into a Capture the Flag (CTF) or War Games match as those can be completed in under 5 minutes. If you're searching and are constantly being put into Team Deathmatch/Assault CTF game types (These match types take 10+ minutes to complete), quit out to the main menu and then go back into matchmaking. It may take a few tries, but eventually the server will give you a CTF or War Games match.Co-op:
These have to be done in "Player Match" and do not count if done in a Private Match. Also, if a player dies at the end of the match and the rest of the party completes the match, the win WILL NOT count for the dead player. A player must be ALIVE at the end of a co-op match in order to pick up a win.
Familiarize yourself with one of the co-op maps and focus on getting all of your wins on that one map. This helps reduce the room for error as enemies will constantly spawn in the same places. We boosted a majority of our wins on Lost Valley (Co-op Map 1).There's a good walkthrough strategy for Lost Valley posted under the "Co-Op 1" achievement.