One Finger Death Punch

As you may know, mastery points are representing accumulated high scores from the levels you are getting, either in campaign or survival modes. So, no matter how many times you replay certain level its score won't add up, only the highest one is adding more. If you want to go purely for those achievements you can get them easier by boosting points in survival levels, and I'm not talking about survival modes, but those levels you stumble upon in the campaign map. You know, those you can skip easy and just let them kill you to continue.

It may sound weird that those survival maps are easier, since you only have 5 health points comparing to 10 you have in the survival mode. But the thing is - after a while bots stop speeding up, unlike in the other mode. While I'm struggling to breach 3000 kills milestone in the survival mode, in the easy campaign map, with some time and effort, I reached over 10000. In fact, I could reach more, but I allowed them to kill me, because earlier there was a bug with the mastery achievements. If you somehow managed to unlock more than one mastery achievement, only the highest one would unlock while the lower one would remain stuck forever. Luckily, devs patched it, so all the achievements are now unlocking retroactively.