It's My Party
Uncommon10.1%GrindOptionalMulti-player
You've hosted and successfully completed 50 team missions from start to finish.
Host and successfully complete 50 team missions, start to finish. So you need to be the host (start a public/private lobby with other players joining) and finish 50 missions with a team. Host public games on popular Hazards to fill your lobby and grind out the 50. A co-op count.