Vertical Drop Heroes HD

Not as hard as you would think. But it requires a bit of luck. What you need is a key and the right caged NPC. The one in question is the dark haired and red red sword wielding fellow. Once free he will hack and slash his way through nearby enemies. All you need is to make sure you do not attack any enemies until the achievement unlocks. After that kill away. Again, first level is the easiest to get this.