Sanguine Bond

Whenever you gain life, target opponent loses that much life.

Typhoid Rats

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

Vampire Nighthawk

Ob Nixilis of the Black Oath

+2: Each opponent loses 1 life. You gain life equal to the life lost this way.
−2: Create a 5/5 black Demon creature token with flying. You lose 2 life.
−8: You get an emblem with "{1}{B}, Sacrifice a creature: You gain X life and draw X cards, where X is the sacrificed creature's power."
Ob Nixilis of the Black Oath can be your commander.

Crypt Ghast

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever you tap a Swamp for mana, add an additional {B}.

Woodland Cemetery

Woodland Cemetery enters tapped unless you control a Swamp or a Forest.
{T}: Add {B} or {G}.

Darkness

Prevent all combat damage that would be dealt this turn.

Consume Spirit

Spend only black mana on X.
Consume Spirit deals X damage to any target and you gain X life.

Ayara, Furnace Queen

At the beginning of combat on your turn, return up to one target artifact or creature card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step.

Ayara, Widow of the Realm

{T}, Sacrifice another creature or artifact: Ayara, Widow of the Realm deals X damage to target opponent or battle and you gain X life, where X is the sacrificed permanent's mana value.
{5}{R/P}: Transform Ayara. Activate only as a sorcery. ({R/P} can be paid with either {R} or 2 life.)

Ayara, Widow of the Realm // Ayara, Furnace Queen

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Defiant Bloodlord

Flying
Whenever you gain life, target opponent loses that much life.

Black Knight

First strike (This creature deals combat damage before creatures without first strike.)
Protection from white (This creature can't be blocked, targeted, dealt damage, or enchanted by anything white.)