Contested Counterspell

You attempt to interrupt a creature in the process of casting a spell. Both you and the creature make a contested d20 test, each adding your respective spellcasting ability and the spell's level (for you, this is the level you cast counterspell at). If your result is equal to or greater than the creature's result, the creature's spell fails and has no effect.

The counterspell cannot itself be counterspelled. However, before any dice are rolled, allies of the creatures involved in the contested counterspell may attempt to lend their aid. If they also cast counterspell, their ally in the contest further adds the spellcasting ability and spell level of the helper(s).