Homebrew accursed Species Details

you are a being of necrotic power merged with the living. It could be that you were killed but at the moment of your death your mind and soul generated a necrotic spark binding you soul to your undead body. Mabey at death a powerful necrotic wave filled your body with energy while burning away most of your essence or you were killed by necrotic damage but you had unfinished business. Whatever the case your body is fuelled by necrotic power. 

accursed Traits

wings of the night- Once per long rest you can sprout a pair of crackling necrotic wings which give you a flying speed of 40 until you dismiss them with a bonus action of attack.