A lunar eclipse during a full moon, or a moon at 80%+ of full, will cause a werewolf to de-transform from their monstrous hairy wolf form during the eclipse. Yet they will maintain their mindless violent werewolf rage while in human causing them to go on a serial killing spree. In addition the blood red color of the moon during an eclipse further enrages them, and increases their power. Luckily this unusual paranormal state only occurs in areas where the eclipse is actually visible. The less of an eclipse effect, the less horrific the mayhem will be.
It’s also rumored that the werewolf Lycanthropia virus is vulnerable during an eclipse and that there’s a chance for a cure. While in the human form with Werewolf persona a restoration of full humanity may be possible through various magics, and perhaps even Cryptozoological anti-viral treatments.