Blast of woe

You Focus necrotic energy into your hand and infuse it with negative energy, the energy takes the appearance of a tortured soul as you blast it at a creature within range. Make a ranged spell attack against the creature to strike it with a blast of sorrow. On a hit, the target takes 1d12 necrotic damage, and it must make a Strength saving throw against your spell DC, on a fail the creature is knocked prone, if saved the creature isn’t knocked prone. 

If you hit an undead target, it also has disadvantage on attack rolls against you until the end of your next turn.

This spell's damage increases by 1d12 when you reach 5th level (2d12), 13th level (3d12), and 18th level (4d12).