Callideus' Balanced Counterspell

You attempt to interrupt a creature in the process of casting a spell. Make an ability check using your spellcasting ability. The DC equals 10 + the difference between the target spell's level and the level of the spell slot used to cast this spell. On a success, the creature's spell fails and has no effect. On a critical failure, the target spell succeeds and has advantage.

At Higher Levels. At seventh level, if a critical success is rolled and succeeds the DC check, the spell's effect is reflected back at the caster.

"He appealed to Mystra regarding what he thought was a fair modification to the weave, but his plea fell on deaf ears."
-New professor of Arcane Studies on why his predecessor quit