According to OP:
Makes the screen flash white and your characters flash black when a counter hit happens. Also has the zoom/white flash on invincibility from my last module, but it's easy to remove anyways.

Download flash.cns and place it inside any folder, usually data/. Put "flash.cns" inside save/config.ini in the Common states category.
Example:
; Common states (CNS or ZSS)
States = data/functions.zss, data/action.zss, [...] data/flash.cns
;
Module v1. Thanks Alceris for the programming assistance