This spell acts as an advanced version of the 3rd level Counterspell.  

When you cast this spell, you are attempting to make a spell a creature is casting have a critical failure and detonate in it's hand , causing the casting creature (and/or objects in it's possession) to be affected by the spell instead of the intended target.  Any AOE spells become single target for the purposes of A'aroc's Premature Thaumaturgical Detonation.  If the spell's initial target was the the casting creature (self), then a feedback loop causes the the spell to dissipate harmlessly with no effect.  Any unusual spells or effects (Telepathy, Arcane Eye, etc) should be adjudicated by the DM to have the most humorous results.

When casting this spell, make an ability check using your spellcasting ability. The DC equals 10 + 2 times the spell's level minus the level A'aroc's Premature Thaumaturgical Detonation is cast at.  On a success, the creature's spell is disrupted and  takes effect on the casting creature instead of the target.

 (example: A Drow is casting a 4th level Ice Storm and you are attempting to detonate it.  You make an ability check using your spellcasting ability with The DC equaling 10 + 2x4 (the spell's level) minus 6 (the level A'aroc's Premature Thaumaturgical Detonation is cast at)  That equals 10 + 8 - 6 = DC 12.  On a success, the creature's Ice Storm is disrupted and the Drow takes 2d8 bludgeoning damage and 4d6 cold damage on a failed save, or half as much damage on a successful one.)

At Higher Levels. When you cast this spell using a spell slot of 7th level or higher, the DC of A'aroc's Premature Thaumaturgical Detonation is adjusted upwards in your favor.