Mage Slayer

Maybe you come from a long line of mage hunters and are continuing your families legacy or maybe you have a grudge against magic casters after a stray Meteor Swarm hit your village. Regardless of what brought you here, you have become the very thing mages fear. A fighter trained to slaughter them and show them the true might of the martial fighters of the world.

Always remember the wise words of the first mage slayer:

"Didn't expect me to parry that did you, ya arcane freak!" 

- Aurthur of Camlann to the Witch Morigan Lefae at the battle of Afthaven.

 

Know Thy Enemy

When you choose this archetype at 3rd level, you gain proficiency in the arcana skill and gain the ability to ritually cast detect magic a number of times equal to your proficiency bonus per long rest.

Anti-Magic Weapon

At 3rd level, you may take an hour to ritually modify a martial weapon you are proficient with, when you do this the weapon gains the ability to "Negate" magic. While wielding this weapon you may, as a reaction, counter spell any spell that comes within 5 feet of you. The counter spell is cast at a level equal to your proficiency bonus (minimum of 3rd level) and can be used a number of times equal to your wisdom modifier (minimum of once). Your number of uses is fully reset on a long rest, however you may regain one charge via short rest once per day.

For the purposes of this feature it is assumed that spells (Unless specified otherwise) travel in a straight line from caster to the target. DM ruling regarding this could change depending on the spell or certain features such as meta-magics. 

DM ruling also applies to whether this feature would be applicable for the Interception fighting style. 

Mages Nightmare

Starting at 7th level, When you cause a mage to break concentration on their spell, they must succeed a wisdom saving throw or be frightened of you until your next turn. The DC for this check is equal to your proficiency bonus + the damage dealt that caused the mage to lose concentration. (This is not all the damage you have dealt to the mage this turn, it is only the damage that caused the concentration to be lost.)

You also receive advantage when trying to intimidate mages, however you have disadvantage on all other charisma skills (Persuasion, Deception, Performance) against mages.  

Target the Mages

Starting at 10th level, when you roll initiative you may make an investigation check to identify enemy mages (the DC is up to DM discretion as every combat situation is different) if you succeed you gain an extra 15ft. of movement in a straight line towards any mage that you identified. This movement does not provoke opportunity attacks and can only be used before the first turn of combat is made but after initiative is rolled. 

Magical Adaptation

Starting at 15th level, if applicable when you negate a spell using your Anti-Magic weapon feature, it triggers a free cast of the Absorb Elements spell at 5th level.

Additionally you gain advantage on DEX checks to avoid spell damage and on a successful DEX check you can reduce the damage you take by your fighter level. 

Anti-Magic Field

Starting at 18th level, while wielding your Anti-Magic Weapon you can use an action to activate an Anti-Magic field around yourself (It can be dismissed for free on your turn). For the next minute you gain a magic negation field in a 10 ft. radius sphere around yourself, spells that enter this radius are instantly counter spelled. When a spell is counter spelled by your field you take damage equal to the spell level, if this damage would cause you to fall unconscious the spell is instead counter spelled for free and your Anti-Magic field is disabled while you gain an exhaustion point. Spell casters who enter this field instantly lose concentration. (This does not trigger your Mages Nightmare feature.)

(The fields affects do apply to every spell and spell caster regardless of their affiliation with you.)

Once you use this feature, you can’t use it again until you finish a long rest.

(An optional ruling is that a wish spell can be cast through the field, however the spells effect would be the opposite of whatever the caster wished for due to the Anti-Magic energies during the casting.)