Realms of Arkania: Star Trail

You can get this achievement by using the combat AI, but it might take a bit longer than doing it manually. Your best bet is to fill your party with mages that use Domination spells like "Horriphobus" and "Be My Friend", as they won't actually kill the enemies. Then find some low-level enemies whom you can direct the spells on. A few bandits or wolves that you run into as you're traveling works well.

Once in combat, make sure you use only these spells. Most of the other fields of magic will still cause damage, and physical attacks will always do this. You also won't be able to control what your characters use in the auto-combat mode, but if your skill level is high enough in these spells, then it should automatically rely on them. Alternatively, you can manually control the battle too. Either way will work provided that you're using the correct spells.

In addition to this, in order to finish the battle without killing anyone, all of the enemies must be contested. Whether they flee from battle, faint, or suffer from any other debilitating effects. You just need to make sure that every enemy can't attack on their turn. Even killing just one will void the achievement. But fortunately, you can do this with really any battle in the game. Once you've finished at least one battle with a pacifist victory, the achievement will unlock.