Cato's Magehunter Orb

You create a shimmering orb of arcane energy at a point you can see within range. The orb floats there for the duration or until triggered.

The next time a hostile spellcaster within 60ft of the orb casts a spell using a spell slot, it zips toward the caster. That spellcaster must make a Dexterity saving throw, taking 8d6 force damage on a failed save or half as much on a successful one. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 3rd.