Oath of Murder

Swear an Oath to slay all those who get in your way. Slay them in Bhaal's name. Embody his will to kill. To commit murder. To kill EVERYONE. Under Bhaal's name you shall be known as a Unholy Assasian.

Bloodlust

After killing and "enemy" you get +6 to hit and 1d8 Necrotic damage for your next three attacks. Every kill thereafter sets the counter back to three and adds an additional +1 to hit and another 1d4 Necrotic damage. When kill an "enemy" with a smite you get another 1d4 bonus Necrotic damage. If you do not kill anything after five hours past from your last kill, you go crazy and attack things on sight until something is killed, or lesser restoration is casted on you successfully. (If the latter happens you go crazy after two hours not five.)

Ways of Murder

Choose two Ways of Murder, you get two at Level 3, another at Levels 5, 8, 11, and 15.

Choices: 

Murder Smites: Smites do an additional 1d10 Necrotic damage.

Fast Kills: Get a +3 Initiative.

Quick Strikes: Can take the attack action as a bonus action.

Counter: Can take the attack action as a reaction if attacked by a melee attack within your weapon's reach.

Blood Smite: 1d10 Necrotic damage, the target must make a CON save or be affected by Blood Loss. (Blood Loss: Take 1d8 damage at the start of their turn. Creatures like Constructs cannot be afflicted with this because they do not have blood.)

Power Strikes: Take a minus -5 to hit but +5 damage.

Blood Sacrifice: Roll up to half of your hit dice, take Necrotic damage equal to amount rolled, but deal the amount rolled in Necrotic damage to next attack.

Eldritch Murder: Learn 2 Warlock Cantrips and 1 1st level spell. If they deal damage, they deal another 1d6 Necrotic damage.

Blood Spear: Summon a spear and you can throw it as a bonus action, it deals 2d6 Necrotic damage.

Murder Weapons: Bind your lust for murder to weapon. It has +3 hit and additional 1d12 Necrotic damage. If it has not drawn blood after 10 hours, it will gain a will and randomly attack someone until they are killed, then this stops. Another way to stop this is to remove the bind, if you do this you cannot bind to the weapon until 5 days past.

Blood Lash: You transform your arm into a blood whip. It deals 2d4 Bludgeoning and 1d6 Necrotic damage, its range is 15ft. This is considered a curse and cannot be removed without the remove curse spell.

Lost Mind: -3 to INT and gain +2 STR, +1 DEX, and +1 CON.

Blood Luck: Add +2 to next hit after successfully hitting a creature that can bleed.

Blood Rage: Get the effects of a Level 1 Barbarian rage, but on every hit, you deal an additional 2d8 Necrotic damage but take 1d8 Necrotic damage yourself.

Aura of Death

All creatures within 15ft of you take 2d10 Necrotic damage. If they are at 10% or less health, they instantly die.

Smite of Doom

When cast a smite all creatures within 35ft must make a WIS save or get the fear condition. They also take 4d12 Necrotic damage at the start of their turn. If upcasted the smite it deals an additional 2d12 Necrotic damage, the WIS save DC increases by 4, and the fear damage increase by 1d12 damage.

SLAYER

Turn into the Slayer. (From the Baldur's Gates games.) It is treated like a Druid's wildshape, Hp 560 + (CON x Hit dice), STR 26, DEX 18, CON 26, INT 8, WIS 8, CHA 8. You have multiattack and can take 8 attacks (Claws 5d12 Slashing and 4d10 Necrotic), Death Brand (Brand a target and they take additional 3d8 Necrotic damage, uses a bonus action.), Blood Slash (5d10 Necrotic damage recover half of damage done to Hp.), Murder Lunge (4d8 bludgeoning damage, replaces jump), Piercing Growl (All creatures must make a DC 26 WIS save or get the feared condition, Bonus Action.)