Bloodletter

Not all people study medicine to heal. Some study it to learn the body's weaknesses and how to better exploit them. Among the black markets, Bloodletters generally use their anatomical expertise as back-alley doctors that ask no questions, or as contractors sent not to merely kill someone, but to cripple it and send a message.

Surgical Precision

When choosing this subclass, your anatomical knowledge allows you to strike in such ways as to deal internal damage:

-You can choose to deal your additional Sneak Attack damage as Psychic or Force, representing either damaging nerves or breaking bones. You choose the damage type when the Sneak Attack lands;

-Additionally, you gain proficiency in Medicine and Herbalism Kit if you don't already have them. If you do, you gain Expertise in either one.

Field Diagnosis

When you choose this subclass, your understanding of the body grants you insight in and out of combat:

-You can use a bonus action to study a creature you can see within 30 feet. Until the start of your next turn, your first Sneak Attack against that creature ignores resistances;

-You can also learn if a creature is currently suffering from a disease, poison, or condition (such as blinded, stunned, or frightened). This doesn't reveal the source, only the presence.

Aggravated Wound

Starting at level 9, once per turn, when you hit a creature with a Sneak Attack, you can choose to apply a status effect as you exploit it's weak points:

-Flinch: the creature is frightened of you until the end of their next turn as it reels from a very painful injury;

-Spasm: the creature must make a CON save (DC=8+Dex modifier+proficiency) or is stunned until the start of their next turn from the shock of getting hit in a nerve bundle;

-Bleed: the creature must make a CON save (DC=8+Dex modifier+proficiency) or, for 1 minute, it takes 1d6 piercing damage after it attacks, as it starts to bleed from a major artery. The creature can repeat the save at the end of their turn to stop the bleeding early.

You can use this feature a number of times equal to your proficiency bonus per long rest.

Hardened to Harm

Starting with level 13, your knowledge of the body includes that of your own:

-You gain immunity to the Poisoned condition, and advantage on saving throws against all other negative effects except for Grappled, Bound and Prone.

-Whenever you spend Hit Dice during a short rest, you may also add your proficiency to each die rolled.

Trauma Mastery

Starting with level 17, you become a master of the life's inner workings and how to stop them.

Once per turn, when you hit a creature with a Sneak Attack, you can force them to make a Constitution saving throw (DC = 8 + Dex modifier + proficiency). On a failure, you choose one:

-The target is Paralyzed until the end of its next turn as you deliver a crippling strike.

-The target is Blinded or Deafened (your choice) for 1 minute from a well placed hit to the head. They can repeat the save at the end of each of their turns.

Additionally, your Sneak Attacks ignore resistance and immunity to damage.