Nullblade

Some rogues learn to pick locks. Nullblades learn to pick apart reality itself. Trained by mage hunters, occult assassins, and anti-arcane factions, these rogues specialize in dismantling magical defenses, studying spellcasters under pressure, and exploiting the flaws hidden inside every spell. To a Nullblade: Mage Armor is predictable geometry. Shield is delayed panic. Concentration is a weakness waiting to collapse. Magic is not sacred. It is vulnerable

Level 3: Arcane Profile

As a Bonus Action, choose one creature you can see within 60 feet. For 1 minute, the creature becomes your Profiled Target. While a creature is Profiled: you know whether it can cast spells, you know its spellcasting ability, and you know the highest level spell it can currently cast. Additionally: when the target casts a spell, you may use your Reaction to identify the spell automatically. You may profile a creature a number of times equal to your Proficiency Bonus per Long Rest.

Breach Defense

When you deal Sneak Attack damage to a creature: Mage Armor provides no benefit against that attack, and magical bonuses to AC from Shield are reduced by 2 against the triggering attack. Additionally: when a creature fails a Concentration saving throw caused by your Sneak Attack, it takes additional Psychic damage equal to your Dexterity modifier

Level 3: Breach Defense

When you deal Sneak Attack damage to a creature: Mage Armor provides no benefit against that attack, and magical bonuses to AC from Shield are reduced by 2 against the triggering attack. Additionally: when a creature fails a Concentration saving throw caused by your Sneak Attack, it takes additional Psychic damage equal to your Dexterity modifier

Level 9: Perceptual Sabotage

When you hit a creature with Sneak Attack, you may force it to make a Wisdom saving throw. On a failed save, until the start of your next turn: the creature cannot take Reactions, it has disadvantage on Concentration checks, and it cannot distinguish you from illusions, invisibility, or magical duplicates. Additionally: your attacks against the creature do not provoke Opportunity Attacks. You may use this feature a number of times equal to your Proficiency Bonus per Long Rest

Level 13: Spellbreaker Instinct

Evasive Interruption When a creature you can see casts a spell targeting only you, you may use your Reaction to move up to half your speed without provoking Opportunity Attacks. If this movement causes the spell to lose line of sight or move you out of range, the spell fails. Arcane Exploitation When a Profiled Target casts a spell: you gain Advantage on the next attack roll you make against it before the end of your next turn. Fracture Concentration When you deal Sneak Attack damage to a creature concentrating on a spell: it subtracts your Proficiency Bonus from its Concentration saving throw

Level 17: Sever the Weave

When you hit a creature with Sneak Attack, you may activate this feature. For 1 minute: the target cannot benefit from Shield, concentration checks are made with disadvantage, and the first spell it casts on each turn deals reduced damage equal to your Sneak Attack dice. Additionally: you always know the target’s location within 120 feet. The creature may repeat a Charisma saving throw at the end of each of its turns, ending the effect on a success. Once you use this feature, you cannot use it again until finishing a Long Rest