The Riffs are around when starting a new city or starting a new game entirely. They show up to, "Impress" the survivors in the Player's outpost. They appear and disappear from time to time, helping with clearing the, "Zed " population. They also wear forest-camo fatigues indicating that they may be what is left of the Army in the post-apocalyptic world of Rebuild 2.
They seem to be major rivals with your rivals as well, the Last Judgement Gang . There is a way to achieve an ending with the help of The Riffs, which is to defeat the Last Judgement Gang at a chosen location. Once the battle is completed, they seemingly dissapear, or they join the Player's outpost, or just left the city due to the fact that they think the Player can handle him/her-self and/or there is nothing else to do with the dispersement of the Last Judgement Gang.