Exquisite Blood

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

Have

Ad Nauseam

Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value. You may repeat this process any number of times.

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Dark Ritual

Swamp

Sickening Dreams

As an additional cost to cast this spell, discard X cards.
Sickening Dreams deals X damage to each creature and each player.

Maralen of the Mornsong

Players can't draw cards.
At the beginning of each player's draw step, that player loses 3 life, searches their library for a card, puts it into their hand, then shuffles.

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if seven or more cards are in your graveyard.

The Soul Stone

Indestructible
{T}: Add {B}.
{6}{B}, {T}, Exile a creature you control: Harness The Soul Stone. (Once harnessed, its ∞ ability is active.)
∞ — At the beginning of your upkeep, return target creature card from your graveyard to the battlefield.