FROGUN

To help people who may think this is glitched, as I did:

Better wording for this achievement would be "finish a level with no enemy being harmed at all". If an enemy dies, e.g. by falling off a ledge, then it invalidates this achievement.

You can get this achievement on the first level of the game by manipulating the enemies to follow you and leaving them in a safe space. If you just run through the level quickly then at least one of the fly enemies will die following you even if you don't touch them.