Bloodline curse

The bloodline curse is an extremely powerfull ritual, first described in Changes, which is used to kill an entire bloodline. The ritual itself involves killing a member of a family, which also brings death to the victim's siblings and parrents, then their siblings and parents, etc. until noone is left. This is the reason why killing the youngest member of a family is the best way to make sure the whole bloodline dies (as it doesn't seem to spread to the children). The bloodline curse also works and vampiric bloodlines, where the "parent" is the vampire who transformed a victim. In Changes, Harry is able to use the prepared curse to obliterate the whole Red Court - by killing it's youngest member, Susan Rodriguez, on the altar.