Arcane Feedback

You attempt to interrupt a creature in the process of casting a spell by blasting it with psychic energy. If the creature is casting a spell of 4th level or lower, its spell fails and has no effect. The creature must also make an Intelligence saving throw. The creature suffers 21 (7d6) psychic damage on a failed save, or half as much damage on a successful one. If it is casting a spell of 5th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect, and must make an Intelligence saving throw or suffer the psychic damage as described before.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the interrupted spell has no effect if its level is less than or equal to the level of the spell slot you used. Additionally, the spell's damage increases by 1d6 for each slot level above fourth.