Graf Rats

At the beginning of combat on your turn, if you both own and control Graf Rats and a creature named Midnight Scavengers, exile them, then meld them into Chittering Host.

Plaguecrafter

When Plaguecrafter enters the battlefield, each player sacrifices a creature or planeswalker. Each player who can't discards a card.

Shadowmage Infiltrator

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
Whenever Shadowmage Infiltrator deals combat damage to a player, you may draw a card.

Gixian Infiltrator

Whenever you sacrifice another permanent, put a +1/+1 counter on Gixian Infiltrator.

Warteye Witch

Whenever Warteye Witch or another creature you control dies, scry 1.

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this turn.

Midnight Scavengers

When Midnight Scavengers enters the battlefield, you may return target creature card with mana value 3 or less from your graveyard to your hand.
(Melds with Graf Rats.)

Endrek Sahr, Master Breeder

Whenever you cast a creature spell, create X 1/1 black Thrull creature tokens, where X is that spell's mana value.
When you control seven or more Thrulls, sacrifice Endrek Sahr, Master Breeder.

Falkenrath Noble

Flying
Whenever Falkenrath Noble or another creature dies, target player loses 1 life and you gain 1 life.

Stronghold Rats

Shadow (This creature can block or be blocked by only creatures with shadow.)
Whenever Stronghold Rats deals combat damage to a player, each player discards a card.

Skyclave Shadowcat

{1}{B}, Sacrifice another creature: Put a +1/+1 counter on Skyclave Shadowcat.
Whenever a creature you control with a +1/+1 counter on it dies, draw a card.

Chittering Witch

When Chittering Witch enters the battlefield, create a number of 1/1 black Rat creature tokens equal to the number of opponents you have.
{1}{B}, Sacrifice a creature: Target creature gets -2/-2 until end of turn.

Viscera Seer

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

Deliberate

Ruin Rat

Deathtouch
When Ruin Rat dies, exile target card from an opponent's graveyard.

Consecrated by Blood

Enchant creature
Enchanted creature gets +2/+2 and has flying and "Sacrifice two other creatures: Regenerate this creature." (The next time the creature would be destroyed this turn, it isn't. Instead tap it, remove all damage from it, and remove it from combat.)

Ravenous Squirrel

Whenever you sacrifice an artifact or creature, put a +1/+1 counter on Ravenous Squirrel.
{1}{B}{G}, Sacrifice an artifact or creature: You gain 1 life and draw a card.

Lolth, Spider Queen

Whenever a creature you control dies, put a loyalty counter on Lolth, Spider Queen.
0: You draw a card and you lose 1 life.
−3: Create two 2/1 black Spider creature tokens with menace and reach.
−8: You get an emblem with "Whenever an opponent is dealt combat damage by one or more creatures you control, if that player lost less than 8 life this turn, they lose life equal to the difference."

Blood Artist

Whenever Blood Artist or another creature dies, target player loses 1 life and you gain 1 life.

Witch's Cauldron

{1}{B}, {T}, Sacrifice a creature: You gain 1 life and draw a card.

Fatal Push

Destroy target creature if it has mana value 2 or less.
Revolt — Destroy that creature if it has mana value 4 or less instead if a permanent you controlled left the battlefield this turn.

Kaito Shizuki

At the beginning of your end step, if Kaito Shizuki entered the battlefield this turn, he phases out.
+1: Draw a card. Then discard a card unless you attacked this turn.
−2: Create a 1/1 blue Ninja creature token with "This creature can't be blocked."
−7: You get an emblem with "Whenever a creature you control deals combat damage to a player, search your library for a blue or black creature card, put it onto the battlefield, then shuffle."

Typhoid Rats

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

Dictate of Erebos

Flash
Whenever a creature you control dies, each opponent sacrifices a creature.

Skirsdag High Priest

Morbid — {T}, Tap two untapped creatures you control: Create a 5/5 black Demon creature token with flying. Activate only if a creature died this turn.

Savra, Queen of the Golgari

Whenever you sacrifice a black creature, you may pay 2 life. If you do, each other player sacrifices a creature.
Whenever you sacrifice a green creature, you may gain 2 life.

Gavony Unhallowed

Whenever another creature you control dies, put a +1/+1 counter on Gavony Unhallowed.

Etrata, the Silencer

Etrata, the Silencer can't be blocked.
Whenever Etrata deals combat damage to a player, exile target creature that player controls and put a hit counter on that card. That player loses the game if they own three or more exiled cards with hit counters on them. Etrata's owner shuffles Etrata into their library.

Witch's Cottage

({T}: Add {B}.)
Witch's Cottage enters the battlefield tapped unless you control three or more other Swamps.
When Witch's Cottage enters the battlefield untapped, you may put target creature card from your graveyard on top of your library.

Drider

Reach
Whenever Drider deals combat damage to a player, create a 2/1 black Spider creature token with menace and reach.

Priest of Forgotten Gods

{T}, Sacrifice two other creatures: Any number of target players each lose 2 life and sacrifice a creature. You add {B}{B} and draw a card.

Piper of the Swarm

Rats you control have menace.
{1}{B}, {T}: Create a 1/1 black Rat creature token.
{2}{B}{B}, {T}, Sacrifice three Rats: Gain control of target creature.

Drana, Liberator of Malakir

Flying, first strike
Whenever Drana, Liberator of Malakir deals combat damage to a player, put a +1/+1 counter on each attacking creature you control.

Plumb the Forbidden

As an additional cost to cast this spell, you may sacrifice one or more creatures. When you do, copy this spell for each creature sacrificed this way.
You draw a card and you lose 1 life.

Bloodmist Infiltrator

Whenever Bloodmist Infiltrator attacks, you may sacrifice another creature. If you do, Bloodmist Infiltrator can't be blocked this turn.

Ravenous Harpy

Flying
{1}, Sacrifice another creature: Put a +1/+1 counter on Ravenous Harpy.

Ruthless Deathfang

Flying
Whenever you sacrifice a creature, target opponent sacrifices a creature.

Vampire Aristocrat

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

Ayara, First of Locthwain

Whenever Ayara, First of Locthwain or another black creature enters the battlefield under your control, each opponent loses 1 life and you gain 1 life.
{T}, Sacrifice another black creature: Draw a card.

Butcher of Malakir

Flying
Whenever Butcher of Malakir or another creature you control dies, each opponent sacrifices a creature.

Soul Stair Expedition

Landfall — Whenever a land enters the battlefield under your control, you may put a quest counter on Soul Stair Expedition.
Remove three quest counters from Soul Stair Expedition and sacrifice it: Return up to two target creature cards from your graveyard to your hand.

Defile

Target creature gets -1/-1 until end of turn for each Swamp you control.

Carrion Feeder

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

Minion Reflector

Whenever a nontoken creature enters the battlefield under your control, you may pay {2}. If you do, create a token that's a copy of that creature, except it has haste and "At the beginning of the end step, sacrifice this permanent."

Bontu's Monument

Black creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, each opponent loses 1 life and you gain 1 life.

Sedgemoor Witch

Menace
Ward—Pay 3 life. (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays 3 life.)
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a 1/1 black and green Pest creature token with "When this creature dies, you gain 1 life."

Ogre Slumlord

Whenever another nontoken creature dies, you may create a 1/1 black Rat creature token.
Rats you control have deathtouch.

Hunt for Specimens

Create a 1/1 black and green Pest creature token with "When this creature dies, you gain 1 life."
Learn. (You may reveal a Lesson card you own from outside the game and put it into your hand, or discard a card to draw a card.)