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As an archetypal Inquisitive, you excel at rooting out secrets and unraveling mysteries. You rely on your sharp eye for detail, but also on your finely honed ability to read the words and deeds of other creatures to determine their true intent. You excel at defeating creatures that hide among and prey upon ordinary folk, and your mastery of lore and your sharp eye make you well equipped to expose and end hidden evils.
Source: Xanathar's Guide to Everything
Ear for Deceit
When you choose this archetype at 3rd level, you develop a keen ear for picking out lies. Whenever you make a Wisdom (Insight) check to determine whether a creature is lying, treat a roll of 7 or lower on the d20 as an 8. Your passive value for this skill increase by 5 at all times.
Eye for Detail
Starting at 3rd level, you can use a bonus action to make a Wisdom (Perception) check to spot a hidden creature or object or to make an Intelligence (Investigation) check. to uncover or decipher clues. Out of combat this allows you to constantly and unobtrusively use these skills without attracting attention. Your passive value in these skills increase by 5 at all times.
At 3rd level, you gain the ability to decipher an opponent’s tactics and develop a counter to them. As a bonus action, you make a Wisdom (Insight) check against a creature you can see that isn’t incapacitated, contested by the target’s Charisma (Deception) check. If you succeed, you gain advantage on attacks against this enemy and that enemy has disadvantage on attacks against you until the start of your next turn. You can use your Sneak Attack against that target even if you don't have advantage on the attack roll, but not if you have disadvantage on it. This benefit lasts for 1 minute or until you successfully use this feature against a different target.
At 9th level, when you have Insightful Fighting active against an enemy that is within 5 ft. of you, allies that attacks that enemy gain advantage, as if you used the Help action to assist their attack. you gain advantage on any Wisdom (Perception) or Intelligence (Investigation) check if you move no more than half your speed on the same turn.
At 13th level, your senses are almost impossible to foil. As an action You sense the presence of illusions, shapechangers not in their original form, and other magic designed to deceive the senses within 30 feet of you, provided you aren't blinded or deafened. You sense that an effect is attempting to trick you, but you gain no insight into what is hidden or into its true nature. You can use this feature a number of times equal to your Wisdom modifier (minimum of once), and you regain all expended uses of it when you finish a long rest.
Eye for Weakness
At 17th level, you learn to exploit a creature’s weaknesses by carefully studying its tactics and movement. While your Insightful Fighting feature applies to a creature, your Sneak Attack damage against that creature increases by 3d6.
This subclass' abilities had way too many restrictions, and all did basically the same thing rather than improving on abilities you already had. I cleaned this up and made the abilities have greater effect as well as creating some synergies.