Mage Slayer (Revised)

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, you can use your reaction *before* the spell is cast to make a melee weapon attack against the creature.
- On a hit, the target must make a Constitution saving throw as if maintaining concentration on a spell (DC 10 or half the damage dealt, whichever is higher).
- On a failure, the creature loses the spell.

- 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.