How does One Hit Kill work?

[Peyote]

I used many trainer on many games but still cant figure it out, how does one hit kill work? Does it give you 99999 damage or 1hp for enemy ?
For example on game ARPG games like titan quest, torchlight, etc.
Thanks

 

[Kalas]

It's enemy HP, you simply change their base HP to let's say 1, and that's it, [1 shot kill]