Spellbreaker

Magic, like all things in the universe, follows rules.  Those who do not comprehend these rules thing magic is an infinite power.  To those that cannot understand magic, it is an unnatural and terrifying force capable of anything.  Magic is to these simple creatures, what a Spellbreaker is to the magically inclined.  Perhaps they are the equal and opposite force to the arcane.  Maybe they are a mistake in the multiverse, a stitch in the infinite tapestry of creation.  Whatever their reason, whatever their origin, they disrupt a world built on magic and terrify those who thought themselves gods.

Mana Static

Magic and you don't get along.  At all.  Starting at the 3rd level, spells that target you suffer a negative modifier to affect or hit you, equal to your proficiency.  At the 7th level, you may choose not to impose this penalty so long as you are conscious.  At the 15th level, you may choose not to impose this penalty even if you are not conscious.

Arcane Disruption

You can feel the strands of magic binding spells together, and with enough focus and force, you can snap them.  Beginning at 7th level, you gain the ability to focus your anti-magical powers on targeted effects.  As a bonus action, you may expend a Hit Die to make a Spellbreaker Check (1d20 + Proficiency + CON) against a magical effect (10 + Spell Level) within 10ft.  If the magical effect is affecting you specifically, such as a targeted effect or a concentration, you may use your reaction and expend a Hit Die instead.

Wrath of the Mundane

In a world of magic, you are a threat to the very fabric of reality.  Your sword cuts deeper, you feel less pain, and the winds of magic seem to blow around you.  Starting at the 10th level, you gain the following benefits.

• Add your constitution modifier to attacks made with non-magical weapons, and to damage dealt with those attacks. 
• Add your constitution modifier to your Armor Class when wearing non-magical armor. 
• Gain resistance to magical damage when you do not have any magical items attuned to you.

Arcane Anomaly

The very essence of magic avoids you, unable to comprehend you.  At 15th level, you have advantage against all magical effects, and you cannot be charmed, even by the mundane.  If you would take half damage from a magical effect you succeed in making a saving throw against, instead you take no damage and suffer no magical effects.

Spellshatter

You understand the flows of magic better than many wizards can hope to, and if they are wise, as much as they can fear.  Starting at 18th level, you may, as reaction, attempt to counter a spell with a successful Spellbreak Check (1d20 + Prof + Con) against the caster's Spell DC (8 + Spellcasting Ability Modifier + Caster's Proficiency Bonus).  If you successfully counter the spell, you may deal a d8 Force damage to the Caster, equal to your proficiency bonus.