Ehershh

Ankhseram Black Magic is a Black Art that allows its user to produce a black miasma that kills anything it touches.[1] However, certain Magic Items, such as Natsu Dragneel's scarf, can protect people from the deadly effects of it.[4] This Magic is uncontrollable at times, causing it to burst out randomly, killing anything within a certain radius of the caster.[5] However, if the user forgets the value of life, they can fully control the Magic.[6] This Magic cannot be learnt, but instead, true to its name as a curse, is brought upon someone by Ankhseram, who may do so to a person making light of the connections between life and death.[2][7] Zeref explained to Mavis that the more regard the cursed individual holds for life then the more they will end up killing inadvertently and only when they no longer have any regards to life will they stop killing at all which led this Magic to be known as the "The Contradictory Curse." The main side effect of this curse is near-absolute immortality, with Zeref remarking that he couldn't kill Mavis and vice versa, even if their heads were separated from their bodies. Additionally, after some time of being afflicted with the curse, the person in question's mental state becomes warped to the point where even their own thoughts, feelings and actions become contradictory as well.