Unholy Apotheosis

You temporarily take the form of some powerful undead, you gain the following:

• You have advantage on Constitution saves against poison and disease

• You cannot be magically aged

• If an Undead tried to attack you or cast a harmful spell, it must throw a Wisdom saving throw. On a fail it must choose a different target. If it can't choose a different target, it has disadvantage on attacking you.

• When you cast this spell and as an action on later turns, you make the creature's soul partly erupt. The creature must make a constitution save or suffer 10d6 Necrotic damage, or half as much on a success.

• You are immune to Necrotic and Poison damage.