Mage Slayer

Complete guide to the Mage Slayer feat in D&D 5e. Punish spellcasters, disrupt concentration, and make enemy mages regret getting close to you.

Benefit

You excel at disrupting spellcasters, gaining reaction attacks when they cast, imposing disadvantage on concentration saves, and gaining advantage on saves against close-range spells.

Mechanics

Mage Slayer provides three anti-caster benefits: **Reaction Attack on Casting:** 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. **Concentration Disruption:** 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. **Advantage on Saves:** You have advantage on saving throws against spells cast by creatures within 5 feet of you. **Important Details:** - Reaction attack happens before the spell completes - Works even if the spell doesn't target you - Concentration disadvantage stacks with other effects - Save advantage only against spells cast within 5 feet - Helps shut down enemy spellcasters in melee

Synergies

Common Mistakes

Common Mistake
Thinking the reaction attack can counterspell - it happens after the spell is cast
Common Mistake
Not positioning yourself next to enemy spellcasters
Common Mistake
Forgetting the concentration disadvantage applies whenever you damage them
Common Mistake
Missing that save advantage only works within 5 feet
Common Mistake
Taking this feat when your campaign has few spellcasters
Common Mistake
Not realizing the reaction can damage them before the spell resolves (but doesn't stop the spell)

DM Tips

DM Tip
Mage Slayer is campaign-dependent - more valuable if many enemies cast spells
DM Tip
Intelligent casters will avoid melee with Mage Slayer users
DM Tip
Teleportation, Misty Step, and Dimension Door help casters escape
DM Tip
This feat is niche but powerful when applicable
DM Tip
Consider mixing melee and ranged casters to challenge Mage Slayer builds
DM Tip
Reaction attack can interrupt some spells if damage breaks concentration on a previous spell

Sources & Further Reading