Step 1: Make them into a metaphor about Batman, about society, or about whatever.
Step 2: Make them dark and twisted, as disturbing as possible.
Step 3: Batman must combat inner demons while fighting them: use this as an opportunity to explore his broken psyche.
Step 4: Shock value, make them commit a disturbing act the readers won't forget.
Step 5: Monologues
Step 6: Profit???