7-level Necromancy (ritual)
You touch a willing creature that is not a shadow creature. That creature gains a Shadow Form, which makes them immune to further Shadowfell Influence. The target becomes temporarily shadowy, gaining a +4 bonus to Stealth checks. While outside of the Shadowfell, the target takes a -4 penalty to attack rolls, saving throws, and ability checks besides. Every time the target finishes a long rest outside of the Shadowfell, the penalty is reduced by 1 until it disappears. The bonus to Stealth is also reduced in this way.