Have

Ruthless Disposal

As an additional cost to cast this spell, discard a card and sacrifice a creature.
Two target creatures each get -13/-13 until end of turn.

Gnawing Zombie

{1}{B}, Sacrifice a creature: Target player loses 1 life and you gain 1 life.

Unlucky Thirteen

Disciple of Perdition

When Disciple of Perdition dies, choose one. If you have exactly 13 life, you may choose both instead.
• You draw a card and you lose 1 life.
• Exile target opponent's graveyard. That player loses 1 life.

Blight Keeper

Flying
{7}{B}, {T}, Sacrifice Blight Keeper: Target opponent loses 4 life and you gain 4 life.

Piranha Marsh

Piranha Marsh enters tapped.
When Piranha Marsh enters, target player loses 1 life.
{T}: Add {B}.

Skirsdag Supplicant

{B}, {T}, Discard a card: Each player loses 2 life.

Tree of Perdition

Defender
{T}: Exchange target opponent's life total with Tree of Perdition's toughness.

Swamp

Tragic Slip

Target creature gets -1/-1 until end of turn.
Morbid — That creature gets -13/-13 until end of turn instead if a creature died this turn.

Soulcage Fiend

When Soulcage Fiend dies, each player loses 3 life.

Sling-Gang Lieutenant

When Sling-Gang Lieutenant enters, create two 1/1 red Goblin creature tokens.
Sacrifice a Goblin: Target player loses 1 life and you gain 1 life.

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Dread Rider

{1}{B}, {T}, Exile a creature card from your graveyard: Target opponent loses 3 life.

Triskaidekaphobia

At the beginning of your upkeep, choose one —
• Each player with exactly 13 life loses the game, then each player gains 1 life.
• Each player with exactly 13 life loses the game, then each player loses 1 life.

Thriving Moor

Thriving Moor enters tapped. As it enters, choose a color other than black.
{T}: Add {B} or one mana of the chosen color.