Blood Priest

Trained heavily in covert combat skills that synergize with their innate blood magic, a Blood Priest treats the blood of their victims as a most sacred sacrifice and use it to enhance their own and their allies' prowess.  Whilst their inherent nature comes across as largely grotesque in nature, they aren't necessarily evil themselves.  For example, a Blood Priest may serve a deity of justice or balance and make a pact with their deity to only ever sacrifice the blood of those who actively seek to fight against or disrupt those values.

Blood Offering

Starting at 3rd level, before you would deal damage with your Sneak Attack dice you can choose to spend up to half of them (round up) to instead perform a sacred ritual to offer the blood of your victim to your deity. When you do so, roll the number of Sneak Attack dice chosen and heal a friendly target within 30ft of you for that amount.  The remaining are used as normal Sneak Attack damage.

You can use this ability a number of times up to two plus your proficiency bonus per short rest.

Bound by Blood

Starting from 3rd level, you can perform a blood pact with a number of allies up to the equivalent of your proficiency bonus.  This blood pact gives you and your allies the following benefits:

• When a bonded ally within 30ft of you takes non-magical damage from a target within 5ft of them, you can use your reaction to cause its attacker to take the same amount of damage as psychic damage.
• When a bonded ally makes an ability saving throw or ability check, you may call upon your deity to bless their attempts by making a blood sacrifice and increase their result by an amount up to 2 plus your Rogue level.  For each point you increase their result by you must roll a d4 and take that as psychic damage.
• During combat, once per turn, you and your bonded allies may call upon your blood pact to increase an attack roll by an amount equal to your Intelligence modifier (minimum of 1).

This blood pact remains on you and your allies until you perform the ritual again, you fall unconscious or you die.  If a bonded ally dies then they will lose the benefits, but the pact remains with the other participants.  The pact also ends if all other participants die except for you.

Blood Craze

Starting at 9th level, you have advantage on all attack rolls made with weapons that deal piercing damage to hit a target that has less than half their total health points remaining.

Bathe in Their Blood

Starting at 13th level, when an enemy within 10ft of you is reduced below zero hit points, you can use a reaction to perform a blood ritual to grant yourself and nearby allies temporary hit points equal to 2d6 plus half the amount beyond zero the enemy was taken (up to a maximum of 2d6 plus your Rogue level).

Ultimate Sacrifice

Starting at 17th level, as an action you can call upon the favour of your deity to attempt to resurrect a fallen creature.  Roll your Sneak Attack dice and a d100.  If the result on the d100 is less than the roll on your Sneak Attack, your deity blesses your ritual and it succeeds.  You take damage equal to your Sneak Attack result as psychic damage and the target creature gains half that amount as hit points.  If this damage would reduce you to zero hit points, you automatically fail your first death saving throw.