Endless One

Endless One enters with X +1/+1 counters on it.

Phyrexian Altar

Sacrifice a creature: Add one mana of any color.

Carrion Feeder

Carrion Feeder can't block.
Sacrifice a creature: Put a +1/+1 counter on Carrion Feeder.

Blade of the Bloodchief

Whenever a creature dies, put a +1/+1 counter on equipped creature. If equipped creature is a Vampire, put two +1/+1 counters on it instead.
Equip {1}

Vish Kal, Blood Arbiter

Flying, lifelink
Sacrifice a creature: Put X +1/+1 counters on Vish Kal, Blood Arbiter, where X is the sacrificed creature's power.
Remove all +1/+1 counters from Vish Kal: Target creature gets -1/-1 until end of turn for each +1/+1 counter removed this way.

Phyrexian Marauder

Phyrexian Marauder enters with X +1/+1 counters on it.
Phyrexian Marauder can't block.
Phyrexian Marauder can't attack unless you pay {1} for each +1/+1 counter on it.

Fain, the Broker

{T}, Sacrifice a creature: Put two +1/+1 counters on target creature.
{T}, Remove a counter from a creature you control: Create a Treasure token.
{T}, Sacrifice an artifact: Create a 2/1 white and black Inkling creature token with flying.
{3}{B}: Untap Fain, the Broker.

Bartolomé del Presidio

Sacrifice another creature or artifact: Put a +1/+1 counter on Bartolomé del Presidio.

Forge, Neverwinter Charlatan

Menace
Ward—Sacrifice a creature.
Forge, Neverwinter Charlatan gets +2/+0 for each Treasure you control.
Whenever one or more players sacrifice one or more creatures, you create a tapped Treasure token. This ability triggers only once each turn.

Martyr's Cause

Sacrifice a creature: The next time a source of your choice would deal damage to any target this turn, prevent that damage.

Shifting Wall

Defender (This creature can't attack.)
Shifting Wall enters with X +1/+1 counters on it.

Bloodflow Connoisseur

Sacrifice a creature: Put a +1/+1 counter on Bloodflow Connoisseur.

Stonecoil Serpent

Reach, trample, protection from multicolored
Stonecoil Serpent enters with X +1/+1 counters on it.

Spawning Pit

Sacrifice a creature: Put a charge counter on Spawning Pit.
{1}, Remove two charge counters from Spawning Pit: Create a 2/2 colorless Spawn artifact creature token.

Fanatical Devotion

Sacrifice a creature: Regenerate target creature.

Drannith Ruins

{T}: Add {C}.
{2}, {T}: Put two +1/+1 counters on target non-Human creature that entered this turn.

Cartel Aristocrat

Sacrifice another creature: Cartel Aristocrat gains protection from the color of your choice until end of turn.

Altar of Dementia

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

High Market

{T}: Add {C}.
{T}, Sacrifice a creature: You gain 1 life.

Viscera Seer

Sacrifice a creature: Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Phyrexian Tower

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

Andúril, Narsil Reforged

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
Whenever equipped creature attacks, put a +1/+1 counter on each creature you control. If you have the city's blessing, put two +1/+1 counters on each creature you control instead.
Equip {3}

Mikaeus, the Lunarch

Mikaeus, the Lunarch enters with X +1/+1 counters on it.
{T}: Put a +1/+1 counter on Mikaeus.
{T}, Remove a +1/+1 counter from Mikaeus: Put a +1/+1 counter on each other creature you control.

Animation Module

Whenever one or more +1/+1 counters are put on a permanent you control, you may pay {1}. If you do, create a 1/1 colorless Servo artifact creature token.
{3}, {T}: Choose a counter on target permanent or player. Give that permanent or player another counter of that kind.

Ashnod's Altar

Ayli, Eternal Pilgrim

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
{1}, Sacrifice another creature: You gain life equal to the sacrificed creature's toughness.
{1}{W}{B}, Sacrifice another creature: Exile target nonland permanent. Activate only if you have at least 10 life more than your starting life total.

Bloodthrone Vampire

Sacrifice a creature: Bloodthrone Vampire gets +2/+2 until end of turn.

Desecration Demon

Flying
At the beginning of each combat, any opponent may sacrifice a creature of their choice. If a player does, tap this creature and put a +1/+1 counter on it.

Hangarback Walker

Hangarback Walker enters with X +1/+1 counters on it.
When Hangarback Walker dies, create a 1/1 colorless Thopter artifact creature token with flying for each +1/+1 counter on Hangarback Walker.
{1}, {T}: Put a +1/+1 counter on Hangarback Walker.