This mode is very similar to horde mode from Gears of War. There are 50 stages of enemies, you have to go through each and everyone to get this achievement. If you fail you will have to start all over again. Now if that didn't sound bad enough. You have to do this with all 3 maps. Beating 50 waves straight is required to complete the "Challenge Master" achievement. This is probably the hardest achievement difficulty wise. It is extremely recommended to even have a fighting chance is that you and your team be above level 40 to have the best nanomachines.