The Killing Curse was invented during the early middle ages, by dark witches or wizards. The curse was created primarily as a means of quickly and efficiently slaying one's opponent in a duel.
Syntax: Avada Kedavra
Effect: Depending on the casters level, they will need to roll a number below a certain threshold to succeed in casting the spell. However, the target must also fail a saving throw in order to be killed.