I've been reading Night Watch by Sergei Lukyanenko and thinking about the games that could be used to play in a setting like this. Mortal Coil comes immediately to mind, but, for now at least, I want something that's both mechanically less complex and something that mechanizes the struggle between free will and the machinations of the waring Others that is present in the book. Reading through the pdf of Don't Lose Your Mind has re-excited me about Don't Rest Your Head, so I thought I'd take a stab at hacking it to play in the Night Watch world. Here's what I've got so far:

Except in the areas noted, all stats/dice function in the same way as the stats/dice they replace in a standard game of DRYH.

The Questions: "What just happened to you?", "What's on the surface?", "What lies beneath?", and "What's your path?" remain unchanged. Replace "What's keeping you awake?" with the following:

How did you become an Other? There are many potential Others, but only those who have stepped into Twilight for the first time have become truly initiated into the War. The event and the choices you make during it also determines whether you have become a Light Other or a Dark Other.

What are you fighting for? All Others that have not become tools of War have someone or something concrete that they are fighting for, something that represents the Light or Darkness for them in a way that motivates them to continue the struggle despite its hardships. For Light Others, this is often centered around protecting something or someone from harm. For Dark Others, this is often centered around preserving something or someone's freedom.

Otherness (replaces Madness): A measure of how much you have lost your humanity to the Light or Darkness and become a tool of that power rather than a free-willed human being.

All Others have a basic set of powers that they can make use of: Seeing into Twilight, Entering Twilight, Manipulation of Humans, etc. They also have their own special Other Talents, the areas in which they are strongest: Shapeshifting, Soothsaying, Healing, etc. These replace the Madness Talent from a standard DRYH game.

When Otherness dominates, the large-scale consequences of your actions become obvious to you for a moment. You know that by acting a certain way you will grant an advantage to your side of the war, and this action is considered to be the "right" way to act, regardless of what its immediate consequences might be.

Mechanically, when Otherness dominates, a course of action is laid before you by the GM that your side wants you to follow. Instead of Fight or Flight responses, you simply have five Otherness boxes and the choice to either Embrace or Reject the suggested action. If you Embrace the action, you check off two of your Otherness boxes. If you choose to Reject the action, you check off one Otherness box and the GM banks one Despair Token as the other side gains a long-term advantage against you. If you have four Otherness boxes checked and you choose an Embrace response, you immediately clear all responses and replace one Discipline die with a permanent Otherness die.

When all three Discipline dice are replaced with Otherness dice, you have become a tool of the Light or Darkness; devoid of humanity and free will, you see only your side's "greater good" and eschew anything that does not contribute directly to it. You are no longer a player character.

Willfulness (replaces Exhaustion): A measure of how fed up you have become with the politics, wars, goals, and deceptions of your own side of the War as it attempts to use you to achieve its goals.

Exhaustion Talents become Human Talents but otherwise remain unchanged.

When Willfulness dominates, the strings of supernatural power within a situation become obvious. Even the most mundane of conflicts are now perceived (whether accurately or not) as maneuvers in the War of Others and all their participants as pawns.

Mechanically, when Willfulness dominates, your current Willfulness dice increase by one. When Willfulness reaches six, you can no longer abide the Treaty that governs the War between the Light and the Darkness. Whether you immediately act on it or not, you have broken the Treaty in your heart, and you are marked as a fugitive in such a way that all Others can immediately perceive it. As with a crash in DRYH, it is potentially possible that an Other can survive this experience and make amends, though it is very unlikely.

Discipline remains unchanged.

This all makes me very happy.