Hey there.

For years I tried to get the last achievement called "Problem Child" where you must kill every npc on almost every level except final two (but the tutorial level counts too).

This game is also known as bugged, people can't (for example) normally kill NPC by mind control of another NPC (hitting by axe/scythe didn't do a thing at all). And this achievement is also bugged. Reeeeallly bugged.

And finally, by experimenting (A LOT) in this game I've managed to boost my "20%" of the achievement completion to "100%" and finally get the last achievement.

A step by step instructions:

1) Disable the "Steam Save Cloud" option, so the Steam won't restore deleted saves (yes, we need to delete them soon);
2) Go to "C:\Users\<your PC name>\AppData\LocalLow\Shiver Games\Lucius II"
3) Delete everything inside this folder.
4) Run the game
5) You will get the empty menu screen (with no registered game profiles), so create the new profile
6) Run the "New Game". You will got to the Tutorial level
7) Finish the tutorial level; at the end you will kill the tutorial guy and get +10% of achievement completion.
8) Quit the game
9) Go back again to "C:\Users\<your PC name>\AppData\LocalLow\Shiver Games\Lucius II"
10) Delete everything inside this folder
11) Run the game...

You need to repeat this option about 10 times (if you have 0% of completion).

Only this solution worked for me. I've tried to finish this game 4 times with different playstyles, I've used cheats, but it didn't helped me at all.

Uh, btw, since the progress is STILL SAVING after disabling Steam Cloud + deleting save files, that means, that the information is stored in Registry. If you're skilled enough you can just somehow edit the registry file and get the achievement from the start. But I personally don't know how, so I just finished the tutorial level 10 times in a row.

Also, if it really helped you, I would appreciate the "awards" on this guide. Thanks!
Have fun!