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.

Typhoid Rats

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

Leechridden Swamp

({T}: Add {B}.)
Leechridden Swamp enters tapped.
{B}, {T}: Each opponent loses 1 life. Activate only if you control two or more black permanents.

Murder

Lich's Mastery

Hexproof
You can't lose the game.
Whenever you gain life, draw that many cards.
Whenever you lose life, for each 1 life you lost, exile a permanent you control or a card from your hand or graveyard.
When Lich's Mastery leaves the battlefield, you lose the game.

Thoughtseize

Target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Read the Bones

Scry 2, then draw two cards. You lose 2 life. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Gather the Townsfolk

Create two 1/1 white Human creature tokens.
Fateful hour — If you have 5 or less life, create five of those tokens instead.

Tree of Perdition

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

Reassembling Skeleton

{1}{B}: Return this card from your graveyard to the battlefield tapped.

Crypt Rats

{X}: Crypt Rats deals X damage to each creature and each player. Spend only black mana on X.