You are considered both Humanoid and Undead for the purpose of spells and effects.
(Note: This can affect things like Turn Undead or protection spells—talk with your DM!)

 Your size is Medium.

Accustomed to the gloom of crypts and moonless nights, you can see in darkness within 60 feet as if it were dim light, and in dim light as if it were bright light. You can’t discern color in darkness, only shades of gray.

You have advantage on saving throws against disease, and you have resistance to necrotic damage.
You don’t need to breathe, and you automatically stabilize when dying unless you are beheaded, incinerated, or exposed to radiant damage at 0 HP.

Once per turn, when you cast a cantrip or spell that targets a hostile creature, you can move 10 feet without provoking opportunity attacks, slipping through the shadows like blood down a blade.
You can use this feature a number of times equal to your proficiency bonus, regaining all uses when you finish a long rest.

You know the minor illusion cantrip.
At 3rd level, you can cast silent image.
At 5th level, you can cast suggestion.

You can cast these spells once per long rest without expending a spell slot.
You can also cast them using any spell slots you have.
Charisma is your spellcasting ability for these spells.

Your vampiric fangs are a natural weapon, considered a simple melee weapon with which you are proficient.

• On a hit, it deals 1d6 piercing damage.
  
  
• You may use your Constitution modifier instead of Strength for attack and damage rolls.
  
  
• While you are below half your hit points, you have advantage on attacks with this bite.
  
  

When you hit a creature that is not a Construct or Undead, you may empower yourself with one of the following effects (your choice):

• Blood Sustenance: Regain HP equal to the piercing damage dealt.
  
  
• Blood Focus: Gain a bonus to your next attack roll or ability check equal to the damage dealt.
  
  

You may use this empowerment a number of times equal to your proficiency bonus, regaining all uses on a long rest.

Sunlight Sensitivity

While in direct sunlight, you have disadvantage on attack rolls, ability checks, and Wisdom (Perception) checks that rely on sight.
If you spend more than 1 hour in direct sunlight, you gain 1 level of exhaustion. This resets after a long rest away from sunlight.

Radiant Vulnerability (Conditional)

If you are reduced to 0 HP by radiant damage, you do not automatically stabilize, and your body begins to disintegrate. You must make death saving throws with disadvantage until healed or revived.

You can speak, read, and write Common, Infernal, and one additional language of your choice (often ancient, noble, or forbidden).