A death blow is any damage dealt to an Avatar who is on death's door, other than on the turn they reached death's door. If you deal a death blow to your opponent's avatar, you win! The damage can come from a strike or any effect that specifically deals damage. Note that attacking their sites causes your opponent's avatar to lose life, which is different from damaging their avatar. Losing life, including due to site damage, does not cause a death blow. If both Avatars suffer a death blow simultaneously (perhaps by one attacking the other), the game is a draw. Alternately, many tournaments declare that simultaneous death blows are ignored, and the game continues.