Mage Killer

You are a hunter and slayer of all who practice spellcraft.
Prerequisite: Arcana proficiency
• Spellcasters that you threaten provoke attacks of opportunity when casting spells in your presence.
• If you harm a spellcaster while they are concentrating on a spell, they suffer disadvantage on the concentration check.
• If you see a creature cast a spell, you gain a bonus of +1d4 on all attack rolls against that creature for one minute.