Spell Overloader

You learned to take risks when casting a spell, putting more magic into it than necessary, to get the chance of a bigger impact.
When you take this feat you gain a maximum of 5 Overload Points, and increase that maximum by 5 when you take this feat again. On a long rest or short rest you regain Overload Points equal to your proficiency bonus.

• When casting a damaging spell you can spend Overload Points up to the spells level, you do so before it's determined whether you hit or not. If the spell has multiple targets you can choose targets equal to the amount of Overload Points spent. You can add/subtract the following amount to the spells damage at those chosen targets: Roll a D20 + your spellcasting modifier - 10. If the total damage of the applied instance is negative, you take the amount of damage as the given damage type.
  (E.g. A cast fireball at 3rd level using 3 Overload Points. You rolled a 12 + spell mod of 2 - 10 = 4. The fireball damage is 30, so the damage total for three chosen targets is 34; A cast magic missile using 1 Overload Point. You roll a 4 + spell mod of 2 - 10 = -4. The chosen dart resulted in a 2 for damage resulting in yourself taking 2 force damage.)