Vian's Shadowy Plague

As an action on your turn, you  make an attack roll against a creature and on a hit a shadowy sludge envelopes them. After 1 hour, they become an undead skeleton. Before they become a skeleton, if they touch anyone else, that person is also infected, with the effect repeated. If a skeleton created by this spell kills something, that creature cannot be revived by anything except for a wish spell. To cure a creature affected by this spell, they must be bathed in holy water at midnight on a full moon. A creature with immunity to necrotic damage cannot be affected by this spell, and cannot be contaminated.