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.

Have

Dark Ritual

Patriarch's Bidding

Each player chooses a creature type. Each player returns all creature cards of a type chosen this way from their graveyard to the battlefield.

Damnation

Destroy all creatures. They can't be regenerated.

Grim Tutor

Search your library for a card, put that card into your hand, then shuffle. You lose 3 life.

Chittering Witch

When this creature enters, 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.

Hero's Downfall

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.

Ogre Slumlord

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

Swamp

Ratcatcher

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
At the beginning of your upkeep, you may search your library for a Rat card, reveal it, put it into your hand, then shuffle.

Sign in Blood

Target player draws two cards and loses 2 life.

Invoke Despair

Target opponent sacrifices a creature of their choice. If they can't, they lose 2 life and you draw a card. Then repeat this process for an enchantment and a planeswalker.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice this artifact: Draw a card.

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.

Night's Whisper

Ashcoat of the Shadow Swarm

Whenever Ashcoat 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.)

Overwhelming Remorse

This spell costs {1} less to cast for each creature card in your graveyard.
Exile target creature or planeswalker.

Typhoid Rats

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

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 token: Add one mana of any color.")

Sol Ring

Gray Merchant of Asphodel

When this creature enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

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.)

Go for the Throat

Patron of the Nezumi

Rat offering (You may cast this spell any time you could cast an instant by sacrificing a Rat and paying the difference in mana costs between this and the sacrificed Rat. Mana cost includes color.)
Whenever a permanent is put into an opponent's graveyard, that player loses 1 life.

Infernal Grasp

Destroy target creature. You lose 2 life.

Unearth

Return target creature card with mana value 3 or less from your graveyard to the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)

Feed the Swarm

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

Mutilate

All creatures get -1/-1 until end of turn for each Swamp you control.

Liquimetal Torque

{T}: Add {C}.
{T}: Target nonland permanent becomes an artifact in addition to its other types until end of turn.

Adaptive Automaton

As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
Other creatures you control of the chosen type get +1/+1.

Charcoal Diamond

This artifact enters tapped.
{T}: Add {B}.

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.

Read the Bones

Scry 2, then draw two cards. You lose 2 life. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Gruesome Realization

Choose one —
• You draw two cards and you lose 2 life.
• Creatures your opponents control get -1/-1 until end of turn.

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.

Mind Stone

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

Diabolic Tutor

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

Toxic Deluge

As an additional cost to cast this spell, pay X life.
All creatures get -X/-X until end of turn.