Minion of the Wastes

Trample
As this creature enters, pay any amount of life.
Minion of the Wastes's power and toughness are each equal to the life paid as it entered.

Necrologia

Cast this spell only during your end step.
As an additional cost to cast this spell, pay X life.
Draw X cards.

Font of Agonies

Whenever you pay life, put that many blood counters on this enchantment.
{1}{B}, Remove four blood counters from this enchantment: Destroy target creature.

Dystopia

Cumulative upkeep—Pay 1 life. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
At the beginning of each player's upkeep, that player sacrifices a green or white permanent of their choice.

Kuro, Pitlord

At the beginning of your upkeep, sacrifice Kuro unless you pay {B}{B}{B}{B}.
Pay 1 life: Target creature gets -1/-1 until end of turn.

Withering Boon

As an additional cost to cast this spell, pay 3 life.
Counter target creature spell.

Marshland Bloodcaster

Flying
{1}{B}, {T}: Rather than pay the mana cost of the next spell you cast this turn, you may pay life equal to that spell's mana value.

Lord of the Forsaken

Flying, trample
{B}, Sacrifice another creature: Target player mills three cards.
Pay 1 life: Add {C}. Spend this mana only to cast a spell from your graveyard.

Defiler of Flesh

Menace
As an additional cost to cast black permanent spells, you may pay 2 life. Those spells cost {B} less to cast if you paid life this way. This effect reduces only the amount of black mana you pay.
Whenever you cast a black permanent spell, target creature you control gets +1/+1 and gains menace until end of turn.

Greed

Unspeakable Symbol

Pay 3 life: Put a +1/+1 counter on target creature.

Staff of Compleation

{T}, Pay 1 life: Destroy target permanent you own.
{T}, Pay 2 life: Add one mana of any color.
{T}, Pay 3 life: Proliferate.
{T}, Pay 4 life: Draw a card.
{5}: Untap this artifact.

Plunge into Darkness

Choose one —
• Sacrifice any number of creatures. You gain 3 life for each creature sacrificed this way.
• Pay any amount of life, then look at that many cards from the top of your library. Put one of those cards into your hand and exile the rest.
Entwine {B} (Choose both if you pay the entwine cost.)

Xander's Pact

Casualty 2 (As you cast this spell, you may sacrifice a creature with power 2 or greater. When you do, copy this spell.)
Each opponent exiles the top card of their library. You may cast spells from among those cards this turn. If you cast a spell this way, pay life equal to that spell's mana value rather than pay its mana cost.

K'rrik, Son of Yawgmoth

({B/P} can be paid with either {B} or 2 life.)
Lifelink
For each {B} in a cost, you may pay 2 life rather than pay that mana.
Whenever you cast a black spell, put a +1/+1 counter on K'rrik.

Toxic Deluge

As an additional cost to cast this spell, pay X life.
All creatures get -X/-X until end of turn.

Bolas's Citadel

You may look at the top card of your library any time.
You may play lands and cast spells from the top of your library. If you cast a spell this way, pay life equal to its mana value rather than pay its mana cost.
{T}, Sacrifice ten nonland permanents: Each opponent loses 10 life.

Bond of Agony

As an additional cost to cast this spell, pay X life.
Each other player loses X life.

Ashiok, Wicked Manipulator

If you would pay life while your library has at least that many cards in it, exile that many cards from the top of your library instead.
+1: Look at the top two cards of your library. Exile one of them and put the other into your hand.
−2: Create two 1/1 black Nightmare creature tokens with "At the beginning of combat on your turn, if a card was put into exile this turn, put a +1/+1 counter on this token."
−7: Target player exiles the top X cards of their library, where X is the total mana value of cards you own in exile.

Doom Whisperer

Flying, trample
Pay 2 life: Surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)