Cold Iron Inquisitor

Inquisition. The art of seeking, and stamping out something of heresy. In this case, the heresy is the amazing, unprecedented power of magic. The cold steel shrugs off such things and crushes them, fueling the divine purpose to snuffing out the weave, for good. Once a world has no magic, surely strife will end...

Mana Drain

Starting at 3rd level, you may shape your very own cold steel. You learn a ritual that creates a magical bond between yourself and one weapon that is made of metal. You perform the ritual over the course of 1 hour, which can be done during a short rest. The weapon must be within your reach throughout the ritual, at the conclusion of which you touch the weapon and forge the bond. The blade becomes cold iron, capable of nullifying magic more effectively. When you use this weapon to score a sneak attack, you may drain a spell slot (or mana) equal to the number of sneak dice rolled.

 

Mana Floes

When you choose this archetype at 3rd level, you gain proficiency in the Arcana and History skills if you don’t already have it. Your proficiency bonus is doubled for any ability check you make that uses either of those proficiencies. Choose from the classic 5 senses: Taste, hearing, sight, smell and touch. You can tell easily if something is considered magical or mundane with this sense. For example, by touching a bookshelf, you might know whenever or not it is a magically imbued objects.

Magic Resistance

At 9th level, while you are holding your bonded weapon, you have advantage on saving throws against magical effects, and spell attacks have disadvantage against you. Additional sources of disadvantage from spell attacks instead give them a -3 to hit you.

Item Diffusion

Starting at 13th level, you have the ability to suppress the magic in even simple items. When you hit a creature with your first sneak attack of the initiative with your bonded weapon, the cold steel suppresses one magical item they are holding or wearing that you can see, as long as that item's rarity is equal to or lower than the weapon you are using. When you drain a spell slot with Mana drain, you may heal for an amount equal to the slot's level. 

However, your own magical items are more strained to output magic. You gain a bonus based on your special Mana floes sense for using less attunement slots that your maximum. The format used will be:

Sense: 1 attunement slot open effect//2 attunement slot open effect

Sight: Your passive perception increases by 2//You can spot targets from a mile away, unaided by a lens

Sound: Your passive perception increases by 2// You gain a +3 to detecting hiding creatures

Smell: You can identify magic items and spells without the need to see or hear them, as per the identify spell as a free action on your turn (once per turn)// You know when spells are being cast without the need to see or hear them

Taste: You automatically detect when you are in a space that is enchanted by magic, and what the effects of that enchantment is// You are immune to effects of magic that enchants spaces, such as the forbiddance spell

Touch: When you touch a magical item, you may immediately gain knowledge about it, as if you had cast the Identify spell// When you touch a magical item or effect, you may learn about it's history, as if you had cast the legend lore spell, except it works on any target. This effect may work on creatures, at a DMs discression.  

Cold Iron Nullifier

Starting at 17th level, you gain an aura of antimagic that wraps around you within 40ft. While inside of the aura, a creature cannot recharge or regain charges of magical abilities, including spell slots, and all creatures gain resistance to damage from magical sources. If a magic item would be consumed, or a spell would be cast in this aura that you can see, you may use your reaction to negate it's effects entirely. 

Your body is also steeled against magical effects: You have evasion against saving throws from magical sources, and magical weapons do not have an effect when they attack you, including any attack or damage bonuses. Magical healing on you is halved.