Here's a basic explanation of how the various types of "pacifist challenge" games are defined on this site, just for categorization purposes:
A game where players have the option to use violence to win the game,
but which is also capable of being completed without killing a single thing. Games that allow players to do this are (at the moment) still relatively rare, so we thought they deserved a category of their own.
Pacifist Challenge Run:
Any game that gives players the latitude to win the game with very few mandatory kills, preferably with the majority of the game winnable without the use of violence. However, if and when the player runs into the obstruction of one or more enemies that the game's designers made it
literally impossible to bypass without some form of deadly confrontation, the games found here still
qualify to be listed as a solid "Pacifist Challenge" run. (After all, the player tried hard to make it a zero-kill run— but if the game design made that purist achievement impossible in just a few places, pacifist challenge players will probably still want to know about the game. A few of our favorite examples of this type of game include the RPGs Baldur's Gate, Two Worlds, and Eschalon: Book I.)
Why Bother With Definitions?
The definition of what constitutes a "pacifist run" game is often pretty nebulous, depending on who you ask. For example, one of our contributors learned the term "pacifist challenge" from an RPG that awarded an in-game achievement for killing under 20 entities (though he managed to win the game without killing anything). Other gamers sometimes even use the term "pacifist run"in an even more technical way to refer to a run that just prohibits certain weapons from being used, but otherwise doesn't even discourage kills or violence at all. We consequently came up with our own simple definitions above, just to categorize the game lists here on our own site.