Grim Surgeon.

You've developed a unique familiarity with knives, bodies, and blood in your line of work. Like a tinkerer's knowledge of clockwork and gears, you've come to an understanding of how bodies are put together instead. Medical experts in rough or war-torn cities and villages may follow this archetype, but so do rogues who take a particular interest in either clerical or necromantic magic. A grim surgeon uses medical knowledge and strange blood magic to dismantle foes, restore allies, and control bodies like puppets.

Level 3 Feature:

Medic.

When you choose this archetype at 3rd level, you gain proficiency in the Medicine skill if you don't already have it. Your proficiency bonus is doubled for any ability check you make that uses this skill.
In addition, your familiarity with blood has become magical, giving you some degree of control over it. As a result, you can use a bonus action to magically stabilize an unconscious creature within 5 feet of you.
You can use this same magic when you apply traditional healing techniques. You can use a bonus action to expend one use of a healer's kit on a creature. When you do, that creature regains hit points equal 1d4 + your proficiency bonus. The creature can't regain hit points from this feature again until it finishes a short or long rest.

Transfusion.

Starting at 3rd level, once on each of your turns when you deal Sneak Attack damage to a creature that isn't a construct or an undead, you gain temporary hit points equal to your Intelligence or Charisma modifier (minimum 1).
When you reach 13th level, you gain temporary hit points equal to twice your Intelligence or Charisma modifier instead. These temporary hit points last until the start of your next turn.

Level 9 Feature:

Field Surgeon.

By 9th level, your medical expertise and blood magic allow you to painlessly mend an ally's wounds using surgical techniques. You decide to use this feature at the start of a short rest, choosing a willing creature within your reach when you do. Roll your Sneak Attack dice and record the result. At the end of the short rest, that creature regains a number of hit points equal to the total of your Sneak Attack dice roll. Once a creature regains hit points from this feature, it can't do so again until it finishes a long rest.

Level 13 Feature:

Toxic Shock.

At 13th level, when you gain temporary hit points from your Transfusion feature, the target of the attack is overcome by a wave of sickness. Until the end of its next turn, the target's speed is reduced by 10 feet, and it has disadvantage on the next attack roll or ability check that it makes before the end of its next turn.

Level 17 Feature:

Bloodbound.

By 17th level, you can command the blood inside certain creatures. Immediately after you deal Sneak Attack damage to a beast or humanoid, you can force that creature to make a Constitution saving throw. The DC is equal to 8 + your proficiency bonus + your Intelligence or Charisma modifier. On a failed save, that creature is under the effect of the Dominate Beast or Dominate Person spell, respectively, for 1 minute or until you choose to end the effect (no action required).
Once you use this feature, you can't use it again until you finish a short or long rest.