Karumonix, the Rat King

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
Other Rats you control have toxic 1.
When Karumonix enters, look at the top five cards of your library. You may reveal any number of Rat cards from among them and put the revealed cards into your hand. Put the rest on the bottom of your library in a random order.

The Dross Pits

This land enters tapped.
{T}: Add {B}.
{1}{B}, {T}, Sacrifice this land: Draw a card.

Ink-Eyes, Servant of Oni

Ninjutsu {3}{B}{B} ({3}{B}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Ink-Eyes deals combat damage to a player, you may put target creature card from that player's graveyard onto the battlefield under your control.
{1}{B}: Regenerate Ink-Eyes.

Coat of Arms

Each creature gets +1/+1 for each other creature on the battlefield that shares at least one creature type with it. (For example, if two Goblin Warriors and a Goblin Shaman are on the battlefield, each gets +2/+2.)

Infectious Inquiry

You draw two cards and you lose 2 life. Each opponent gets a poison counter.

Crypt Rats

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

Urborg, Tomb of Yawgmoth

Each land is a Swamp in addition to its other land types.

Vraan, Executioner Thane

Whenever one or more other creatures you control die, each opponent loses 2 life and you gain 2 life. This ability triggers only once each turn.

Falkenrath Noble

Flying
Whenever this creature 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 this creature deals combat damage to a player, each player discards a card.

Jet Medallion

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

Feast of the Unicorn

Enchant creature
Enchanted creature gets +4/+0.

Diabolic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Feed the Swarm

Destroy target creature or enchantment an opponent controls. You lose life equal to that permanent's mana value.

Extractor Demon

Flying
Whenever another creature leaves the battlefield, you may have target player mill two cards.
Unearth {2}{B} ({2}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Septic Rats

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever this creature attacks, if defending player is poisoned, it gets +1/+1 until end of turn.

Mind Swords

If you control a Swamp, you may sacrifice a creature rather than pay this spell's mana cost.
Each player exiles two cards from their hand.

Cabal Coffers

{2}, {T}: Add {B} for each Swamp you control.

Prophetic Prism

When this artifact enters, draw a card.
{1}, {T}: Add one mana of any color.

Order of Yawgmoth

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
Whenever this creature deals damage to a player, that player discards a card.

Razortooth Rats

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)

Relentless Rats

This creature gets +1/+1 for each other creature on the battlefield named Relentless Rats.
A deck can have any number of cards named Relentless Rats.

Rancid Rats

Skulk (This creature can't be blocked by creatures with greater power.)
Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

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.

Dark Ritual

Nezumi Ronin

Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)

Doom Blade

Drainpipe Vermin

When this creature dies, you may pay {B}. If you do, target player discards a card.

Go for the Throat

Nighteyes the Desecrator

{4}{B}: Put target creature card from a graveyard onto the battlefield under your control.

Nezumi Graverobber

{1}{B}: Exile target card from an opponent's graveyard. If no cards are in that graveyard, flip this creature.

Nezumi Graverobber // Nighteyes the Desecrator

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if seven or more cards are in your graveyard.

Ruin Rat

Deathtouch
When this creature dies, exile target card from an opponent's graveyard.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Feebleness

Flash
Enchant creature
Enchanted creature gets -2/-1.

Thriving Rats

When this creature enters, you get {E}{E} (two energy counters).
Whenever this creature attacks, you may pay {E}{E}. If you do, put a +1/+1 counter on it.

Sphere of Annihilation

This artifact enters with X void counters on it.
At the beginning of your upkeep, exile this artifact, all creatures and planeswalkers with mana value less than or equal to the number of void counters on it, and all creature and planeswalker cards in graveyards with mana value less than or equal to the number of void counters on it.

Butcher of Malakir

Flying
Whenever this creature or another creature you control dies, each opponent sacrifices a creature of their choice.

Touch of Death

Touch of Death deals 1 damage to target player or planeswalker. You gain 1 life.
Draw a card at the beginning of the next turn's upkeep.

Bog Rats

Corrupt

Corrupt deals damage to any target equal to the number of Swamps you control. You gain life equal to the damage dealt this way.

Soul Feast

Target player loses 4 life and you gain 4 life.

Cruel Grimnarch

Deathtouch
When this creature enters, each opponent discards a card. For each opponent who can't, you gain 4 life.

Typhoid Rats

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

Blood Artist

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

Twisted Embrace

Enchant artifact or creature you control
When this Aura enters, destroy target creature or planeswalker an opponent controls.
As long as enchanted permanent is a creature, it gets +1/+1.

Smallpox

Each player loses 1 life, discards a card, sacrifices a creature of their choice, then sacrifices a land of their choice.

Zulaport Cutthroat

Whenever this creature or another creature you control dies, each opponent loses 1 life and you gain 1 life.

Marrow-Gnawer

All Rats have fear.
{T}, Sacrifice a Rat: Create X 1/1 black Rat creature tokens, where X is the number of Rats you control.

Treasure Chest

{4}, Sacrifice this artifact: Roll a d20.
1 | Trapped! — You lose 3 life.
2—9 | Create five Treasure tokens.
10—19 | You gain 3 life and draw three cards.
20 | Search your library for a card. If it's an artifact card, you may put it onto the battlefield. Otherwise, put that card into your hand. Then shuffle.

Sinister Strength

Enchant creature
Enchanted creature gets +3/+1 and is black.

Gutter Skulk

Unholy Strength

Enchant creature
Enchanted creature gets +2/+1.

Thought Vessel

You have no maximum hand size.
{T}: Add {C}.

Ob Nixilis, Unshackled

Flying, trample
Whenever an opponent searches their library, that player sacrifices a creature of their choice and loses 10 life.
Whenever another creature dies, put a +1/+1 counter on Ob Nixilis.

Pack Rat

Pack Rat's power and toughness are each equal to the number of Rats you control.
{2}{B}, Discard a card: Create a token that's a copy of this creature.

Mind Rot

Rise from the Grave

Put target creature card from a graveyard onto the battlefield under your control. That creature is a black Zombie in addition to its other colors and types.

Swamp

Ravenous Rats

When this creature enters, target opponent discards a card.

Nezumi Cutthroat

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
This creature can't block.

Burglar Rat

When this creature enters, each opponent discards a card.

Phyrexian Arena

At the beginning of your upkeep, you draw a card and you lose 1 life.

Thornbite Staff

Equipped creature has "{2}, {T}: This creature deals 1 damage to any target" and "Whenever a creature dies, untap this creature."
Whenever a Shaman creature enters, you may attach this Equipment to it.
Equip {4}

Markov Dreadknight

Flying
{2}{B}, Discard a card: Put two +1/+1 counters on this creature.

Swarmyard

{T}: Add {C}.
{T}: Regenerate target Insect, Rat, Spider, or Squirrel. (The next time it would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Death Stroke

Annihilating Glare

As an additional cost to cast this spell, pay {4} or sacrifice an artifact or creature.
Destroy target creature or planeswalker.

Portal to Phyrexia

When this artifact enters, each opponent sacrifices three creatures of their choice.
At the beginning of your upkeep, put target creature card from a graveyard onto the battlefield under your control. It's a Phyrexian in addition to its other types.

Shadowspear

Equipped creature gets +1/+1 and has trample and lifelink.
{1}: Permanents your opponents control lose hexproof and indestructible until end of turn.
Equip {2}

Greel, Mind Raker

{X}{B}, {T}, Discard two cards: Target player discards X cards at random.

Rat Colony

This creature gets +1/+0 for each other Rat you control.
A deck can have any number of cards named Rat Colony.