Mutations are just ways Valve is making acheivements easier. I have played Single Player Versus with cheats, and the bots are idiots, and it would make it easy to get S.I. acheivements, but to do so you use to have to enabled sv_cheats 1 so you could not get the acheivements, but now with these mutations, you can easily get versus acheivements now against stupid bots.