Base Class: Rogue
Horrifying assassins who have acquired great knowledge regarding the biology of the creatures they hunt. They are able to strike at foes with ruthless, bloody attacks that leave them in pain. Dreg letters study the sight, smell, and texture of blood to investigate enemies. They enjoy drawing it from creatures, and by doing so can learn about the qualities of their victims rapidly. Death follows them and they welcome it with open arms
Surgical Gouging
Starting at 3rd level when you take this archetype, when you make an attack that meets the conditions to apply your sneak attack damage to a target and haven't dealt your sneak attack damage already this turn, you can instead force the creature to make a Constitution saving throw (DC 8 + your Dexterity modifier + your proficiency bonus). If they fail, they take 1d4 damage slashing damage at the start of each of their turns. This ongoing damage lasts for 1 minute, during which you also deal an extra 1d4 damage to them each time you hit them with a ranged weapon attack, or a weapon with the light or finesse properties. A creature may reattempt the saving throw at the end of each of their turns, ending the effect on a success. This feature cannot affect constructs, elementals, or incorporeal creatures like ghosts. If you successfully inflict this condition on a creature, you cannot use your sneak attack damage that turn. A creature cannot suffer from multiple instances of this feature. If multiple creatures inflict this condition on a single target they all gain their extra damage on weapon attacks against them, but the creature only takes the highest amount of ongoing damage among those with the feature. The ongoing damage at the start of their turn and extra damage dealt with your weapons raises to 1d6 at 7th level, 1d8 at 11th level, 1d10 at 15th level, and 1d12 at 19th level. You may use this feature an amount of times equal to your Dexterity modifier + 1 (minimum 1) and regain expended uses when you complete a short or long rest. A use is only considered expended when a creature fails their saving throw.
Blood Telling
Starting at 9th level, when you deal your sneak attack damage to a creature, you may subtract multiples of 1d6 damage from your sneak attack to gain information about that creature based on qualities extrapolated from their blood and the difficulty in extracting it. For each 1d6 you forego, you may acquire one of the following pieces of information: The creature's AC (including armor bonus). Any two of the creature's ability scores, including if they are proficient in saving throws with those ability scores. Details about a trait you're at least somewhat aware they have. The creature's resistances, vulnerabilities, damage immunities, or condition immunities (pick one). The creature's type(s). Approximately how much health the creature has left ("almost full", "about three quarters", "about half", or "about one quarter" depending on which is appropriate)
Taxing Percision
Starting at 13th level, when you make a weapon attack against a creature currently under the ongoing effects of your surgical gouging feature, you have advantage on your attack roll caused by your attacks forcing the creature to twist and move in ways that worsen the wound. Whenever you hit a creature under the effect of your surgical gouging feature and you deal more than 10 damage on a single hit, the ongoing damage they take from surgical gouging increases by 1 (up to a maximum of half your rogue level, rounded down).
Extra Attack
Beginning at 13th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.
Evisceration
Starting at 17th level, if you hit a creature that is currently being affected by your surgical gou ging feature with a weapon attack that would trigger your sneak attack damage, you may force that creature to attempt a Constitution saving throw (DC 8 + your Dexterity modifier + your proficiency bonus) as part of your attack. If you do this, you must use your sneak attack damage on the result of that attack whether they fail or succeed the saving throw. If they fail, the ongoing effects of your surgical gouging end and your attack automatically becomes a critical hit. If the creature fails the saving throw by 5 or more points they are also stunned until the start of their next turn