Counter Strike

In response to a creature missing an attack against you, you can cast a spectral blade that hits the target in response to their attack. The blade hits the target dealing 2d4 slashing damage. The hit creature must make a Constitution saving throw. Becoming stunned until the start of the creature's next turn on a failed save. On a successful save the creature is not stunned.

If cast at 4th level or higher, the slashing damage of the blade increases by 1d4 for every slot level above 3rd.