It’d be good to get a full fireteam of four together and work on Gambit triumphs. There’s a few that having friendly (read: not mote-greedy) teammates are essential:
There’s three triumphs where all four teammates drop blockers on the other team simultaneously - small, medium, large;
There’s three triumphs to send multiple of the same type blockers over, solo. Gotta get 10 small, 10 medium, 6 large in a match.
Edit: one last secret triumph I just read about: One player on the team has to deposit 100 motes without losing any. Definitely a fireteam-cooperative sort of thing.