Mage Slayer

You have practiced techniques useful in melee combat against spellcasters, gaining the following benefits:

• When a creature within 5 feet of you casts a spell, and you have taken an action yet, or have not attempted to qualify for a reaction since taking your action, you gain a free reaction against that spellcaster to use as you see fit (which usually means attacking).
• When you damage a creature that is concentrating on a spell, that creature has disadvantage on the saving throw it makes to maintain its concentration.
• You have advantage on saving throws against spells cast by creatures within 5 feet of you.