In both settings, the Horrors have corrupted astral space, the source of magical power.  The corruption is much more severe in Camrish than in Boston.  Anybody who can access that power instintively filters the pure Karma from the Taint: the result is he Personal Essence Pool.  Most such characters also have a Peripheral Essence Pool: power they can draw on, but which isn't yet filtered and cleaned.  Using that pool has serious negative side effects:

* You start to glow (same progression as in normal Exalted: see SystemReference for the table).

* You start to glow in astral space, potentially attracting the attention of a Horror.  This is accompanied by bits of your body slipping into duality with Astral Space: Horrors and unmanifested spirits will be able to see and affect you.  You can sometimes see them too, out of the corner of your eye, or feeling a tendril slip inside your skin.

* Gaining Limit/Taint near a Horror may enable it to use some powers near you, akin to its spending some of your Limit.  See below.

* The words Limit and Taint are used indistinguishibly.

*  When your Limit hits 10, you limit break (if an Adept) and it resets
  (whether or not you're an Adept).  If you're Horror Marked at the
  time, worse things may happen; again, Horror Marks are quite rare
  and show up as plot devices, not as generic weapons.

<h3>As you pick up Taint...</h3>
Before making your daily Conviction roll, you may instead declare that you're trying to get rid of Taint instead.  Roll your Conviction with a difficulty of your Limit; if you succeed, you may remove a single point of Limit.

When you have 10 temporary Taint, you lose it all and, most of the time, *absolutely nothing happens* (Well, almost nothing.  Most people blow off a little steam: see the Limit Break mechanic from Exalted).  If you happen to be Horror Marked at the time, you gain a point of perminant Taint.  Horrors can spend temporary taint (theirs or yours) to do bad things to you, like penalizing your dice pools by your perminant taint, or adding it to your difficulty, or dealing it to you in damage, or use it to cancel your spending willpower, or other such nastiness.  Getting rid of perminant taint is an endeavor worthy of a quest.

When you're Horror Marked, there's a chance that a Horror can take control of you: When your temporary Taint exceeds your permanent Willpower, it can spend a point of Taint to make you roll your Willpower vs. it's Taint.  If you lose, the horror takes control of you for a scene.  Getting unMarked involves destroying the Horror or getting rid of all your Permanent Taint.

If your Permanent Taint exeeds your Willpower, a Horror can take control of you at the drop of a hat &mdash; this may be the sorry lot of Cadavermen.

See Thorns in Wraith: The Oblivion for examples of neat horror temptation powers.  In addition to the possession mentioned above, be aware that other players may be drafted to play the Horror's voice in the back of your character's head.  Also, they have the ability to offer you extra dice for an action; accepting causes you to accumulate a point of Taint for each 1 rolled.  Don't get addicted...

<h3>Other ways to acquire Taint</h3>
Expect NPCs in Camrish to know that brightly glowing people have been doing Dangerous Magic and should be avoided.  Educated NPCs will know that glowing people are potentially Horror Marked.

What causes you to get temporary Taint points?  Mostly stress: being a Hero is hard, and it's much easier to accumulate gobs of power and use it to be a jerk &mdash; just look at powerful people in real life.  There are two ways for most people to get Taint points: if you have to fail a Virtue roll to avoid acting virtuously, and get successes on that roll, you can spend a point of Willpower and accept a point of Taint to ignore your Virtue for that situation.  Second, pick a "Preferred Taint" for your character (a.k.a. a Virtue Flaw).  It will have a condition attached, like "innocents suffering" or "publicly insulted."  When that condition occurs, you must roll the Virtue associated with that condition and take that many Taint points.

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This is an official mechanic.  Comments here are welcome, but please leave hacking to ExaltedHackingTaint.