Once per battle
Free action to cast
A nearby creature you can see casts a spell.
The nearby creature casting a spell.
Intelligence + Level vs. MD
The target's spell is canceled, and the caster loses the action they were using for the spell. If the spell had a limited use, that use is expended if your natural attack roll is even.
You can now cast counter-magic twice per battle.
You can now cast counter-magic in reaction to a creature using any magical ability, not just casting a spell.