Deep Magic Volume 2 (p.160)
Damage Echo
3-level Transmutation
Casting Time: 1 reaction, which you take when a friendly creature you can see within range deals damage to another creature with an attack that targets only one creature
Range/Area: 30ft.
Components: Verbal, Somatic
Duration: 1 round
Damage/Effect: Damage
You pull an echo of the triggering attack out of the timestream, causing the attack to damage its target twice. All damage dice and modifiers for the triggering attack are rolled twice, and the attackās target takes damage equal to the total. The friendly creature that triggered this spell then has disadvantage on attack rolls until the end of its next turn.
Available for: Sorcerer, Wizard