Bloodletter

Some rogues train to be deadly killers, some master manipulators. Bloodletters train with the grim blood arts. By draining their foes, rogues that follow this archetype enhance their stealth and agility with that energy. As a Bloodletter, you may have stolen your power from a vampire lord, or learned the blood arts through a dark ritual. Some bloodletters just believe that all those at the tip of their blade need to have their blood purged from their body. Your abilities allow you to mark the hearts of your foes, drain the blood of the living, and control of the hearts of others.

Acupuncture

Starting at 3rd level, you gain the ability to mark your foes' hearts with your weapon. Immediately after you hit, but before you deal your Sneak Attack damage to a creature on your turn, you can apply a Heart Mark to that creature as long as it has blood. A Heart Mark lasts for 1 minute, or until a marked creature is reduced to 0 hit points. You can only have one creature marked at any time. When you damage a marked creature on subsequent turns, you can choose to deal extra damage, in exchange for opening your defenses to them.

When you hit a marked creature, you can choose to change your Sneak Attack damage to blood damage. When you do so, you deal an extra 1d6 blood damage to the creature. The amount of the extra damage increases as you gain levels in this class: to 2d6 at 9th level, to 3d6 at 13th level, and to 4d6 at 17th level. You don't need advantage on the attack roll to use your Sneak Attack against a marked creature as long as you don't have disadvantage on the attack roll. All the other rules for Sneak Attack still apply to you. In exchange, you must pay a blood price. Marked creatures have advantage on all attack rolls against you, and advantage on ability checks made to know your location.

You can apply your Heart Mark a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Phlebotomist

When you choose this archetype at 3rd level, you gain proficiency in Medicine, as well as alchemist's supplies and the herbalism kit. If you already have any of these proficiencies, you gain proficiency with one other of your choice of the same type.
In addition, you can make a Wisdom (Medicine) check to stabilize a dying creature as a bonus action, and you can add your Dexterity modifier to the total.

Sparking Cruor

Starting at 9th level, you learn how to spread your bloodletting in unusual ways. Immediately after you deal blood damage to a creature marked by your heart mark, you can cause the blood spray to splash onto another foe. A creature of your choice within 20 feet of the marked creature must succeed on a dexterity saving throw (DC equal to 8 + your proficiency bonus + your Dexterity modifier). If the save fails, the target takes 1d6 blood damage and is bleeding until the end of your next turn.

Grume Drain

By 13th level, you've learned how to enhance the draining effect of your heart marks. A marked creature takes 1d4 blood damage at the start of each of their turns, and has disadvantage on any saving throw to avoid the bleeding condition.
In addition, you can use your action on your turn to drain some of your own blood and end one effect on yourself that is causing you to be poisoned or diseased. You take 1d4 blood damage immediately after.

Combat Surgery

When you reach 17th level, you are no longer limited to having one marked target at a time. In addition, any creature marked by you has vulnerability to blood damage.