Bloodsucker

A scarring experience with a mad mage or a creepy fascination that has spiraled out of control has lead to you becoming obsessed with blood and its use, and through your fascination and experience, along with some questionable practices, you have learned how to wield it to your advantage.

Bloodletting weapons

At 3rd level when you pick this archetype, you gain a set of natural weapons, either in the form of sharp claws for fingers or a set of razor sharp canine teeth. You are proficient with these weapons, they deal 1d4 piecing damage, they cannot be disarmed, and they have the light and finesse properties. 

You can choose to make a special attack with these weapons if the target is grappled, restrained, willing, or incapacitated. You can attempt to drain the blood of the creature with this attack, making a melee weapon attack against it using these natural weapons. If you hit, you deal 1 piercing damage and 1d6 necrotic damage. The target’s hit point maximum is reduced by an amount equal to the necrotic damage taken, and you regain hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. The necrotic damage increases to 2d4 at level 9, 2d6 at level 13, and to 2d8 at level 17.

When you wield daggers as weapons, the damage die of the daggers increases to 1d6, increasing to 1d8 at level 9,  1d10 at level 13, and 1d12 at level 17.

Hemophage Transformation

Starting from level 3 you can use other's blood to transform into near perfect copies of them. If you drink someone's blood, your gain the ability to transform into them as if by the true polymorph spell. You can maintain this transformation up to a number of minutes equal to the amount of the targets blood that was drunk in ounces. You cannot transform into a creature that does not have the same basic arrangement of limbs, you cannot transform into anything with a CR rating higher than your player level, you gain no benefits from any spellcasting features they may possess, and you cannot transform into a creature that possesses legendary resistances or actions. Whilst transformed, you look and sound exactly like the person you transformed into, and can choose to add to this transformation by adding the clothes that they where wearing when you acquired their blood. You gain no magical benefits from these items and they melt into a pile of gray goo when you transform back. While transformed, you retain your mental ability scores and alignment/personality. A person can determine that you are not who you say you are by a successful (insight) check against your (deception) check.

At later levels, certain restrictions on this ability are broken. At level 9, you may transform into a creature even if it does not have the same basic arrangement of limbs. At level 13, you may choose to exchange one of your mental ability scores for the targets whilst you are transformed. At level 17, you may gain the benefits of any spellcasting features the creature would normally possess.

Extractor Cables

From level 9, your study of blood and constant need for it in combat has lead to the development of specialized equipment suited to the task. Over the course of a long rest, you may make up to 2 blood extractor cables. These cables possess long clear tubes with a large needle and small pump system on the end, linked to a pack on your back for storing blood. The cables count as weapons that deal 1d6 piercing damage with the reach, special, and finesse properties. When you attack with these cables, you can choose for them to remain lodged in the target's body, and as a bonus action on subsequent turns whilst they are lodged in, may extract their blood, with each cable extracting enough to fill one vial, which will be filled immediately if there is a free vial on your person. A creature may attempt to remove these cables as if they were trying to escape being grappled, making either a Strength (Athletics) or Dexterity (Acrobatics) check contested by your Strength (Athletics) check.

Blood Frenzy

At level 13, the sight of your enemies blood is enough to drive you into a frenzied state of of attack. As a bonus action on your turn, you may target a creature that is below its maximum hit points and have it make a Wisdom (Insight) check contested by your Charisma (Intimidation) check. On a success, you have advantage on attack roles against that target for 1 minute, and you gain 10ft of movement speed when moving towards them. On each of your subsequent turns, you must move so that you end your turn closer to the target than you were at the start of your turn. If you fail to do this, the ability ends. You may do this a number of times per long rest equal to your charisma modifier.

Improved Practices

At level 17, you have achieved the pinnacle of your skills, and can now reliably damage most creatures with your equipment. When using any weapons mentioned in this class, you may switch the damage type to force damage.