Effect: Throughout history, various cultures attributed mystical significance to the menstrual cycle. Many of these myths carried stigmas against menses, due to the unhealthy fears of men in power.
With this Merit, your character still produces menstrual blood. Once per night, she can produce a viscous, dark blood. If she uses this blood in casting a Crúac ritual, she benefits from the 8-again quality. If she touches it to a person before affecting them with a Discipline, they suffer her Blood Potency as a penalty to their Resistance.
Drawback: The character must identify as female. If she draws forth her Undead Menses multiple times in an evening, each beyond the first causes her a level of aggravated damage. As well, any attempts to identify her by her menstrual blood gain a +5 die bonus.