Team fortress 2 has players running around in a box arena to achieve objectives between the opposing RED and BLU teams and you get to choose one of 8 class soldier, heavy, demo-man, scout, sniper, spy, medic, or engineer
the essence is team work because while you can use skill to survive combat encounters (to a degree), each type is too compromised in some way to go it alone like in halo or call or duty: modern warfare to achieve objectives with regularity
each team fights for the RED or BLU side of Mann.co
but in Mann vs Machine, its all about 6 players fending off this:
Hey, I notice that you licensed your sprite as CC BY-NC-ND 3.0, I was wondering if this was a mistake or not?
The Desktop-Ponies-Team page says all the sprites are CC BY-NC-SA 3.0 and if the original standing image was CC BY-NC-SA 3.0, then this would also have to be CC BY-NC-SA 3.0 since it's a derivative work.
Oh yeah. Well I set up the license before I knew much about it and before Desktop Ponies ever thought of licenses. So it wasn't under any license at that time, but yeah, I see no problem with derivative work being allowed