I thought a while ago that Exalted would work best when given an angle, combined with another idea to make it into what the storyteller wants it to be. This resulted in my background for the character the Ghostwalker, and many of my ideas about the Neverborn and the Underworld.
This game style is a combination of Exalted and not surprisingly the Cthulhu Mythos, including the video and roleplaying games based on it.
Each player starts with a number of Sanity Points. Having high Permanent Willpower reduces the chance of losing Sanity. As a character's Sanity approaches zero they become increasingly disturbed. When their Sanity reaches zero they become completely mad and lose all Permanent Willpower and gain a derangement. The higher their Willpower was at the time of losing their Sanity the more severe the derangement is.
There are two possible ways of resolving Sanity loss. Either use the Exalted system of using the character's Willpower as difficulty or a penalty. This is more flexible, for instance you can use Vitues to add temporarily to the character's Willpower but also carries possibility of greater Sanity from especially large threats. It's a more predictable system since low level threats could be ignored by someone with reasonable Willpower. Another system is based on Vampire where the character's Willpower is the minimum number required for a success. This makes a character more resistant to greater Sanity loss but still means they could be affected by minor threats. Another system is where like in Call of Cthulhu each threat has a dice eg. D3, D6, D8 etc. where you could add a fixed modifier eg. +1, and if they score higher than the character's Willpower the difference is the Sanity loss. You may have pre or post roll modifiers where a post roll modifier only applies if the initial roll succeeds. A similar system could be used as an alternative method of damage resolution. Eg. damage 2D6 + 4
If they suffer further Sanity loss they continue to experience the effect of mental dying health levels. Use the difficulty of the character's highest (their primary) Virtue for difficulty of Sanity loss rolls. Each loss of Sanity in this state inflicts loss of a 'phantom' health level and a -1 internal penalty on all of the character's dice rolls. The madness is now eating away at their psyche. When they lose a number of health levels equal to their highest Virtue their mind is irrevocably destroyed causing pathological suicidal behaviour (killing themselves with the nearest thing possible) or homicidal mania that will inevitably result in death. Only potent mind altering Charms can retore (or more disturbingly reduce) a character's mind when they are losing mental health levels or their mind has been lost forever.
Abyssals can inflict a similar direct effect on someone's psyche with the Charm Chakra Violating Blow. The difficulty to lose their last mental health level is their Virtue Rating plus all the levels lost so far. This is the difficulty of undoing the last core element of someone's psyche.
