Cleave

While you are touching a creature with your palm or fist, you can spend a bonus action to roll a d20. Depending on the spell slot level you cast it at, you multiply the final roll by the spell level. If the target of the spell were to be killed by the damage that the attack would do, you can then choose to consume all spell slots of that level to kill the opponent instantly. If the spell cannot instantly kill the opponent or you choose not to, it does nothing.

Using a Higher-Level Spell Slot. The multiplier increases by 1 for every higher spell slot than 1.