Every time a hitpoint is subtracted from a character, the Damage Character Filter will be called if it is specified in the list of Special Locations in CSBuild's Global Information Dialog.
The filter receives the following information:
0 - The character index (0, 1, 2, or 3)
1 - The Character's fingerprint
2 - The Raw damage
3 - Actual damage that will be applied to the character's hitpoints
4 - Mask (Don't know what this is - used to compute actual damage)
5 - P4 (Don't know what this is - used to compute actual damage)
6 - Flags (All zero right now)
The Filter can change parameter 3 and the result is the amount that will be subtracted from the character's hitpoints.