How much time has passed since the first attempt to complete this fucking achievement, I started with the classic part of MPN, there were many attempts, but every time I lost all the progress of the game and one day I just gave up on it, and later the flash stopped working. I thought I would never complete this achievement again, but after a long time developing MPN2, I have a new chance. After beating the game a few times, I started doing this achievement and spent a couple of months playing an hour a day and killing 500-700 people. And hooray, after so many years I've done it!

And yet, it cost me a bad back, as stated in the description of the achievement, although my back hurt long before the game was released :(.