The Symbiote

You've made a pact with some blood fiend, an abomination that feeds on other fiends like a vampire. Or perhaps you made your pact with a vampire directly. Not quite like other fiends, blood fiends are a strange conglomeration of elemental, fiend, and monstrosity; these creatures were first created by Haemnathuun, the Blood Lord. Whether you strive to further its blood thirst or not, your patron grants you many gifts typical of its kind.

Expanded Spell List

The Symbiote lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Fiend Expanded Spells

Spell Level	Spells
1st	cause fear, wrathful smite
2nd	calm emotions, phantasmal force
3rd	fear, summon shadowspawn
4th	phantasmal killer, confusion
5th	fearless wit, dispel evil and good

Vampiric Intimidation

Starting at 1st level, when you cause a hostile creature to become frightened, you gain temporary hit points equal to your charisma modifier.

Stalwart Hemostasis

Starting at 6th level, your patron grants you the toughness typical of its kind. You are immune to the frightened condition.

In addition, you regain 1 hit points if you have no more than half of your hit points left at the start of each of your turns. You don't gain this benefit if you have 0 hit points.

Overwhelming Terror

Starting at 10th level, you can exert your patron's power by inflicting terror by sight alone. As an action, each creature of your choice within 30 feet of you that can see you must succeed on a Wisdom saving throw against your warlock spell save DC or become frightened of you until the end of your next turn. If a creature fails its saving throw by 5 or more, it is stunned while frightened in this way.
You can use this feature a number of times equal to your proficiency bonus, regaining all expended uses when you finish a long rest.

In addition, any creature that would be immune to a fear effect caused by your warlock features or spells now is not immune, but has advantage on the saving throw to resist the effect instead. If a creature normally immune to frightened succeeds on a saving throw against frighten caused by your warlock spells or features, they take 1d6 psychic damage.

Dark Transfusion

Starting at 14th level, you gain the ability to convert other freshly-slain creatures into blood fiends, temporarily binding them to you. If a humanoid, fiend, or elemental is reduced to 0 points within 30 feet of you, you can use your reaction to cause its body to morph into an abomination of blood and flesh, as a Blood Fiend. 

Roll initiative for the blood fiend, which has its own turns. It obeys your verbal commands. While under your command, the blood fiend has immunity to blood damage and the bleeding condition. The blood fiend remains in your service for 10 minutes, at which point it melts into a pool of thick blood.

Once you bind a blood fiend with this feature, you can't use the feature again until you finish a long rest.