Counter-magic

Close-quarters spell
Once per battle
Action: 
Free action to cast
Trigger: 
A nearby creature you can see casts a spell.
Target: 
The nearby creature casting a spell.
Attack: 
Intelligence + Level vs. MD
Hit: 
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.
Champion Feat: 

You can now cast counter-magic twice per battle.

Epic Feat: 

You can now cast counter-magic in reaction to a creature using any magical ability, not just casting a spell.