Phyrexian Altar

Sacrifice a creature: Add one mana of any color.

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, Son of Yawgmoth.

Grave Pact

Whenever a creature you control dies, each other player sacrifices a creature of their choice.

The Golden Throne

Arcane Life-support — If you would lose the game, instead exile The Golden Throne and your life total becomes 1.
A Thousand Souls Die Every Day — {T}, Sacrifice a creature: Add three mana in any combination of colors.

Phyrexian Tower

{T}: Add {C}.
{T}, Sacrifice a creature: Add {B}{B}.

Vampire Hexmage

First strike
Sacrifice Vampire Hexmage: Remove all counters from target permanent.

Tatterkite

Flying
Tatterkite can't have counters put on it.

Jar of Eyeballs

Whenever a creature you control dies, put two eyeball counters on Jar of Eyeballs.
{3}, {T}, Remove all eyeball counters from Jar of Eyeballs: Look at the top X cards of your library, where X is the number of eyeball counters removed this way. Put one of them into your hand and the rest on the bottom of your library in any order.

Mikaeus, the Unhallowed

Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
Whenever a Human deals damage to you, destroy it.
Other non-Human creatures you control get +1/+1 and have undying. (When a creature with undying dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

Lesser Masticore

As an additional cost to cast this spell, discard a card.
{4}: Lesser Masticore deals 1 damage to target creature.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Fraying Omnipotence

Each player loses half their life, then discards half the cards in their hand, then sacrifices half the creatures they control of their choice. Round up each time.

Render Inert

Remove up to five counters from target permanent.
Draw a card.

Triskelion

Triskelion enters with three +1/+1 counters on it.
Remove a +1/+1 counter from Triskelion: It deals 1 damage to any target.

Altar of Dementia

Sacrifice a creature: Target player mills cards equal to the sacrificed creature's power.

Sol Ring

Price of Betrayal

Remove up to five counters from target artifact, creature, planeswalker, or opponent.

Jet Medallion

Black spells you cast cost {1} less to cast.

Aether Snap

Remove all counters from all permanents and exile all tokens.

Walking Ballista

Walking Ballista enters with X +1/+1 counters on it.
{4}: Put a +1/+1 counter on Walking Ballista.
Remove a +1/+1 counter from Walking Ballista: It deals 1 damage to any target.