Unbound Saga has local as well as Xbox Live co-op. This achievement can be earned either way and each episode is pretty easy and straightforward and should take around 7-10 minutes. The achievement will unlock at the statistics screen at the end of the level.
This can also be unlocked by replaying the same episode over and over. Once again episode nine is the shortest at only a little over 4 minutes. If you don't have a second controller or a co-op buddy, you can find one here: Achievement Trading Thread.