Unstable Disruption

You attempt to interrupt a creature in the process of casting a spell. If the creature is casting a:

• cantrip, roll 1d3.
• spell of 1st level or higher, roll 1d4.
• spell of 2nd level or higher, roll 1d6.
• spell of 3rd level or higher, roll 1d8.
• spell of 4th level or higher, roll 1d10.
• spell of 5th level or higher, roll 1d12.
• spell of 6th level or higher, roll 1d20.
• spell of 9th level or higher, roll 1d100.

After you see the result, you can choose to either add or subtract your full spellcasting ability modifier. On a 2-3, the creature's spell fails and has no effect, and you regain your Reaction.