Death curse

A death curse is perhaps the most powerfull spell that a wizard can cast, at the moment of his death. It is first mentioned in Storm Front.

Description
A death curse utilizes all the power a wizard can access, and is cast at the moment of his death.

The curse's target is often the wizard's killer, but it can apparently be directed at anyone, regardless of the target's involvement or physical presence.

Storm Front
In Storm Front, Harry Dresden warns Bianca St. Claire that if she were to kill him like she wants to right there and then, that his death curse would take her down with him.

Death Masks
In Death Masks, Harry Dresden uses his death curse as a threat in an attempt to dissuade Paolo Ortega from his duel challenge.

Blood Rites
In Blood Rites, Bob states that to make a spell long-lasting, it needs to be anchored. To anchor it to a person, it needs to be a blood relation. Margaret LeFay could have anchored her death curse on Lord Raith to Dresden so that as long as he was alive, the spell was still viable.

Dresden learned that Margaret LeFay cursed Lord Raith on her deathbed, preventing him from feeding, and thus prevented him from gaining strength.

Later, Dresden would use this knowledge to his advantage by causing Lord Raith to use up his reserves and getting him to monologue about it while Lara Raith was hiding close enough nearby to hear him.

Dead Beat
In Dead Beat, during Harry Dresden's meeting with the Wardens at McAnally's Pub, Morgan mentions that he witnessed four different death curses in a single day while battling with the Red Court in Sicily.

Later, the former Denarian, Quintus Cassius, before being killed by Mouse at Harry Dresden's orders, hit Dresden with his death curse. He wanted his curse to kill Dresden, but he was too weak to manage that and so settled with cursing Dresden to "die alone".

Changes
In Changes, Dresden recalled Cassius' death curse when he was laid up in St. Mary's with a broken back an he was all alone in the dark feeling utterly helpless. Later, Dresden used the threat of his death curse to destroy Chichén Itzá in order to push the Red King into encouraging Arianna Ortega to answer Dresden's challenge to a duel per the Code Duello. Dresden recalls Cassius' death curse again while floating in Lake Michigan—a familiar voice tells it to "hush now".