Curse of the Twin Princes

You reach out and steal the essence and image of your foe, causing enemies and allies alike to have difficulty distinguishing who is who.  Make a range spell attack against one humanoid creature within range.  If you miss, the target takes 5d10 psychic damage, it cannot take reactions until the start of its next turn, and the spell ends.  If you hit, the target takes 10d10 psychic damage and you steal fragments of the targets identity, incorporating them into yourself for the duration. 

While this effect lasts, any time you take damage you instead take half damage and the target takes the other half as psychic damage.  At the end of each of the targets turns it may make a Charisma saving throw to end this effect.  However, whenever the target makes this save successfully, you may use your reaction to contest its save by making a Charisma check of your own.  You are considered proficient for this check.  If your Charisma check exceeds the result of the targets saving throw, it fails its saving throw instead of succeeds.  

Whenever you are within 10ft of the target while this effect lasts, other creatures have difficulty telling the two of you apart.  Any attacker that targets either you or the target of this spell when you are less than 10ft apart must make a Wisdom saving throw.  If it fails the attacker has a 50% chance of hitting the wrong person.  

The spell ends if you lose concentration, if the target dies, or if you dismiss the effect as a bonus action.