Mage Slayer

When a creature within 5 feet of you casts a spell, you can use your reaction to make a melee weapon attack against that creature.
* 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.
Appears In: 5e Players Handbook