A completely full conversion of the world not being the original ck3 map and there own lore, and some evil elf’s like these In this new world, the evil elves could be known as the "Umbric Elves" or "Shade Elves," their pure black skin and red eyes serving as outward markers of their corrupted nature. These Umbric Elves wield dark and twisted forms of magic, drawing power from the shadows and the depths of their malevolence.
If an Umbric Elf were to breed with a normal elf, their offspring might inherit a trait known as "black blood." This trait grants them resistance to dark magic and the ability to harness and manipulate shadows for defensive purposes. As they grow, they might learn to control their inherited darkness, using it to protect themselves and others from the malevolent influence of their Umbric lineage. They could also be a symbol of good and bad for some other elf’s, the description of the trait could be “ this character’s blood flows with the power of both dark and good magic, being cursed for life.
And well that’s all I’m happy for some more suggestions for it.