I met two opponents 浩色 and his mate from Indonesia. I guess they queue at specific server at the same time so that they can play together in a row of 14-18 FFA games. And before that they team together in 2v2.
Is FFA teaming violate any rule? Their behavior gives unfair advantage, and affect gaming experience of other players.
im going to say yes, its would be like diplomacy in the empire earth days … have to use your mates to kill them off them off then fight it out after they are wiped off the map… or just not join and host your own game
I still don’t know if they violate any code of conduct. (Code of Conduct - Age of Empires) There is a line:
Engaging in behaviors to purposefully undermine matches goes against the spirit of the game.
As they purposefuly workaround the queue system to let them play together, and also team together in a surpose to be 1v1v1v… FFA game, I gave it a try to report them. let’s see how it goes.
Unfortunately, there will always be people “screwing” FFA games. It is only desirable to “make team” when a player performs a wonder or tries to win a victory. Obviously, EVERYONE (who actually play for real) will attack the player who is trying to beat everyone at the same time 
With the “dominion” (“king”) mode, it’s even easier to ruin the game, because just use the “reveal kings” feature and the team can choose easily one by one to kill