I came back this morning after a bit of a stay-cation, and realized my Legendary had yet to beat Belloq. So, off I went to The Sook, stood outside his tent, and hit "Team Up." Within a few minutes, two players and I were hacking away at Belloq, and we won. One of those players and I have been traveling through Zafaria together, helping one another quest and level.
Sometimes, it takes awhile, but Team Up works. I used it on my Promethean for the end of Azteca, and had a full form all the way through. Excellent addition to the game, KI.