Lucifer's Vessel

Your desire, nay, your need to save your wife from your patron's hands has led you into making all sorts of deals... Your latest and greatest one involving Lucifer...

As a Bonus Action, you synchronize your energy with Lucifer's and become a vessel for his power. You remain a vessel for 1 minute. While you are a vessel, you appear to be Lucifer himself. You gain the ability to release a ray of knowledge and essence of hell that deals 20d10 + 54 force damage as an action. This ray forces the target to make a Charisma Saving Throw equal to your Spell Save DC. On a fail, the target takes full damage and is Stunned for two turns. On a success, the target takes half damage and is not Stunned. If the target is Immune to the Stunned condition, they instead take double the damage dealt regardless of if they saved or failed. You can use this ray a number of times equal to half your charisma bonus rounded up, which resets each time you transform. This ray does not benefit from Spell Lord's damage die nor the Spell Save DC increase. This ray cannot be countered and it doesn't work in anti-magic areas.

You can become a vessel twice per long rest, gaining a level of exhaustion every time you revert back into your original form.

Whilst you transform, you don an appearance similar to the First Fallen. Your skin becomes paler, your eyes turn red and your hair black. You sprout black feathered wings and grow two black horns. Your teeth sharpen to a point. While you are out of the transformation, you can communicate with Lucifer (RP flavour like Venom). Whilst you are transformed, it is Lucifer speaking through you.