Lord Skitter, Sewer King

Whenever another Rat enters the battlefield under your control, exile up to one target card from an opponent's graveyard.
At the beginning of combat on your turn, create a 1/1 black Rat creature token with "This creature can't block."

Thrumming Stone

Spells you cast have ripple 4. (Whenever you cast a spell, you may reveal the top four cards of your library. You may cast spells with the same name as that spell from among the revealed cards without paying their mana costs. Put the rest on the bottom of your library.)

Cabal Coffers

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

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.

Species Specialist

As Species Specialist enters the battlefield, choose a creature type.
Whenever a creature of the chosen type dies, you may draw a card.

Sol Ring

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.

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Night's Whisper

Echoing Return

Return target creature card and all other cards with the same name as that card from your graveyard to your hand.

Rat Colony

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

Jet Medallion

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

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.

Gruesome Fate

Each opponent loses 1 life for each creature you control.

Phyrexian Tower

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

Diabolic Intent

As an additional cost to cast this spell, sacrifice a creature.
Search your library for a card, put that card into your hand, then shuffle.

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, Servant of Oni 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.)

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Twisted Sewer-Witch

When Twisted Sewer-Witch enters the battlefield, create a 1/1 black Rat creature token with "This creature can't block." Then for each Rat you control, create a Wicked Role token attached to that Rat. (If you control another Role on it, put that one into the graveyard. Enchanted creature gets +1/+1. When this Aura is put into a graveyard, each opponent loses 1 life.)

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.

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 the battlefield, 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.

Go for the Throat

Myriad Landscape

Myriad Landscape enters the battlefield tapped.
{T}: Add {C}.
{2}, {T}, Sacrifice Myriad Landscape: Search your library for up to two basic land cards that share a land type, put them onto the battlefield tapped, then shuffle.

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 the battlefield, you may attach Thornbite Staff to it.
Equip {4}

Deadly Rollick

If you control a commander, you may cast this spell without paying its mana cost.
Exile target creature.

Bitter Triumph

As an additional cost to cast this spell, discard a card or pay 3 life.
Destroy target creature or planeswalker.

Caged Sun

As Caged Sun enters the battlefield, choose a color.
Creatures you control of the chosen color get +1/+1.
Whenever a land's ability causes you to add one or more mana of the chosen color, add one additional mana of that color.

Exquisite Blood

Whenever an opponent loses life, you gain that much life.

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Thought Vessel

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

Secret Salvage

Exile target nonland card from your graveyard. Search your library for any number of cards with the same name as that card, reveal them, put them into your hand, then shuffle.

The Black Gate

As The Black Gate enters the battlefield, you may pay 3 life. If you don't, it enters the battlefield tapped.
{T}: Add {B}.
{1}{B}, {T}: Choose a player with the most life or tied for most life. Target creature can't be blocked by creatures that player controls this turn.

Rise of the Dark Realms

Put all creature cards from all graveyards onto the battlefield under your control.

Haunted One

Commander creatures you own have "Whenever this creature becomes tapped, it and other creatures you control that share a creature type with it each get +2/+0 and gain undying until end of turn." (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.)

Damnation

Destroy all creatures. They can't be regenerated.

Beseech the Mirror

Bargain (You may sacrifice an artifact, enchantment, or token as you cast this spell.)
Search your library for a card, exile it face down, then shuffle. If this spell was bargained, you may cast the exiled card without paying its mana cost if that spell's mana value is 4 or less. Put the exiled card into your hand if it wasn't cast this way.

Swamp

Infernal Grasp

Destroy target creature. You lose 2 life.

Necropotence

Skip your draw step.
Whenever you discard a card, exile that card from your graveyard.
Pay 1 life: Exile the top card of your library face down. Put that card into your hand at the beginning of your next end step.

Swarmyard

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

Nykthos, Shrine to Nyx

{T}: Add {C}.
{2}, {T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

Crypt Ghast

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever you tap a Swamp for mana, add an additional {B}.

Foul-Tongue Shriek

Target opponent loses 1 life for each attacking creature you control. You gain that much life.

Corrupted Conviction

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Bojuka Bog

Bojuka Bog enters the battlefield tapped.
When Bojuka Bog enters the battlefield, exile target player's graveyard.
{T}: Add {B}.

Ogre Slumlord

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

Deadly Dispute

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards and create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Feed the Swarm

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

Ashcoat of the Shadow Swarm

Whenever Ashcoat of the Shadow Swarm attacks or blocks, other Rats you control get +X/+X until end of turn, where X is the number of Rats you control.
At the beginning of your end step, you may mill four cards. If you do, return up to two Rat creature cards from your graveyard to your hand. (To mill a card, put the top card of your library into your graveyard.)

Phyrexian Arena

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

Demonic Tutor

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

Reliquary Tower

Throne of Eldraine

As Throne of Eldraine enters the battlefield, choose a color.
{T}: Add four mana of the chosen color. Spend this mana only to cast monocolored spells of that color.
{3}, {T}: Draw two cards. Spend only mana of the chosen color to activate this ability.

Crypt Rats

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

Nashi, Moon Sage's Scion

Ninjutsu {3}{B} ({3}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Nashi, Moon Sage's Scion deals combat damage to a player, exile the top card of each player's library. Until end of turn, you may play one of those cards. If you cast a spell this way, pay life equal to its mana value rather than paying its mana cost.