Force Cyclone was a Dark Force power that enabled the user to send a large gust of wind at a victim. The gust contained small droplets of poison. When the poison came in contact with the victim, it started to affect them instantly, slowly disabling their circulatory system. Force Cyclone was rarely used by Sith because of the noticeably long time to use it. But if mastered, it could be performed fairly quickly.
A Force Cyclone user could also replace the deadly poison with something more custom, like acid or lightning. However, if a user tried to combine their custom cyclone with another, it would kill them.