Up The Ante

You hold two dice in your hand, and drop them onto a flat surface. You feel the magic either strengthen or drain you.
Roll 2d20, whichever result is further from 10 is the one you take. If the number is above 10, you add it to your next damage roll. If the number is below 10, you subtract it from your next damage roll.

(Ex: Cast at 1st level. Roll 2d20. Results are 16 and 7. Add 16 to your next damage roll. (16 is 6 away from 10, and 7 is only 3.)) (Ex #2: Cast at 3rd level. Roll 2d20. Results are 12 and 3. -3+9=6. Add 6 to your next damage roll.) 

At Higher Levels. You add a +3 to the result for each slot above 1st level.