Anyone know how to unlock the necro-4 skin?

so I'm trying to get all my unlocks and I came across this skin it says it unlocks through a mission but doesn't give me any more information beyond that and looking into Google I can't even find any evidence this skin even exists which makes me think something is wrong would anyone know what I have to do to unlock it? I'm thinking it's a dlc item but I'm not sure any help is welcome 😁