Blade of the Shadows

You cast the spell over the blade and the metal becomes cold to touch with frost crystals forming along its edge. Hitting a melee attack with this weapon against a creature within 5 feet of you causes the following: 
▬ The target suffers the weapon attack’s normal effects, and you can cause dark black tendrils of shadow to leap from the target to a different creature of your choice that you can see within 5 feet of it.
▬ The second creature takes cold damage equal to your spellcasting ability modifier.

This spell’s damage increases when you reach certain levels. At 5th level, the melee attack deals an extra 1d8 cold damage to the target on a hit, and the cold damage to the second creature increases to 1d8 + your spellcasting ability modifier. Both damage rolls increase by 1d8 at 11th level (2d8 and 2d8) and 17th level (3d8 and 3d8).