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.)

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)

When Blightbelly Rat dies, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Changeling (This card is every creature type.)

As Bloodline Pretender enters the battlefield, choose a creature type.

Whenever another creature of the chosen type enters the battlefield under your control, put a +1/+1 counter on Bloodline Pretender.

Bog Rats can't be blocked by Walls.

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.

When Burglar Rat enters the battlefield, each opponent discards a card.

Changeling (This card is every creature type.)

Changeling Outcast can't block and can't be blocked.

When Chittering Rats enters the battlefield, target opponent puts a card from their hand on top of their library.

Corrupted -- Sacrifice an artifact or creature: Draw a card. Activate only if an opponent has three or more poison counters and only once each turn.

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.

Each player sacrifices a nontoken creature. Roll a d20 and add the toughness of the creature you sacrificed this way.

1--14 | Return a creature card put into a graveyard this way to the battlefield under your control.

15+ | Return up to two creature cards put into graveyards this way to the battlefield under your control.

Whenever a creature you control dies, you draw a card and you lose 1 life.

Menace

As an additional cost to cast black permanent spells, you may pay 2 life. Those spells cost {B} less to cast if you paid life this way. This effect reduces only the amount of black mana you pay.

Whenever you cast a black permanent spell, target creature you control gets +1/+1 and gains menace until end of turn.

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield under its owner's control."

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

Target creature gets -4/-4 until end of turn. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control and you create a Treasure token." (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Until end of turn, target creature gains "When this creature dies, return it to the battlefield tapped under its owner's control with a +1/+1 counter on it."

If it's not your turn, you may exile a black card from your hand rather than pay this spell's mana cost.

Destroy all creatures that entered the battlefield this turn.

Each opponent's maximum hand size is reduced by one.

When Gnawing Vermin enters the battlefield, target player mills two cards.

When Gnawing Vermin dies, target creature you don't control gets -1/-1 until end of turn.

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

When Ichor Rats enters the battlefield, each player gets a poison counter.

As Icon of Ancestry enters the battlefield, choose a creature type.

Creatures you control of the chosen type get +1/+1.

{3}, {T}: Look at the top three cards of your library. You may reveal a creature card of the chosen type from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

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

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.

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

{1}{B}: Regenerate Kuro's Taken.

Each opponent's maximum hand size is reduced by two.

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.

Ninjutsu {1}{B} ({1}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)

Lifelink

Enchant creature you control

Enchanted creature has toxic 2. (Players dealt combat damage by it also get two poison counters.)

When enchanted creature dies, return that card to the battlefield under your control.

Nezumi Bladeblesser has deathtouch as long as you control an artifact.

Nezumi Bladeblesser has menace as long as you control an enchantment. (It can't be blocked except by two or more creatures.)

{B}, Sacrifice a creature: Target player discards a card. Activate only as a sorcery.

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

Nezumi Cutthroat can't block.

Ninjutsu {1}{B} ({1}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)

When Nezumi Prowler enters the battlefield, target creature you control gains deathtouch and lifelink until end of turn.

{1}{B}, {T}: Target opponent discards a card. Then if that player has no cards in hand, flip Nezumi Shortfang.

At the beginning of each opponent's upkeep, that player loses 1 life for each card fewer than three in their hand.

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

Rats you control have deathtouch.

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 Pack Rat.

Pestilence Rats's power is equal to the number of other Rats on the battlefield. (For example, as long as there are two other Rats on the battlefield, Pestilence Rats's power and toughness are 2/3.)

Each opponent gets a poison counter. Then each creature your opponents control gets -1/-1 until end of turn for each poison counter its controller has.

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

Trample

Whenever a source deals damage to Phyrexian Obliterator, that source's controller sacrifices that many permanents.

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.

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.)

Rat Colony gets +1/+0 for each other Rat you control.

A deck can have any number of cards named Rat Colony.

When Ravenous Rats enters the battlefield, target opponent discards a card.

Relentless Rats gets +1/+1 for each other creature on the battlefield named Relentless Rats.

A deck can have any number of cards named Relentless Rats.

Until end of turn, target creature gets +1/+0 and gains lifelink and "When this creature dies, return it to the battlefield tapped under its owner's control."

Deathtouch

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

{T}: Exile the top card of target player's library. If it's a land card, you gain 1 life.

Landfall -- Whenever a land enters the battlefield under your control, you may untap Scrib Nibblers.

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Whenever Septic Rats attacks, if defending player is poisoned, it gets +1/+1 until end of turn.

{3}{B}{B}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)

As long as Sinuous Vermin is monstrous, it has menace. (It can't be blocked except by two or more creatures.)

Ninjutsu {B} ({B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)

Whenever Skullsnatcher deals combat damage to a player, exile up to two target cards from that player's graveyard.

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.

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control."

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Swarm of Rats's power is equal to the number of Rats you control.

When Thieves' Tools enters the battlefield, create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Equipped creature can't be blocked as long as its power is 3 or less.

Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

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

Target creature gains undying until end of turn. (When it 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.)

Until end of turn, target creature gains "When this creature dies, return it to the battlefield tapped under its owner's control with a +1/+1 counter on it."

Whenever another artifact or creature you control is put into a graveyard from the battlefield, put an oil counter on Vat of Rebirth.

{2}{B}, {T}, Remove four oil counters from Vat of Rebirth: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.

Trample

When Wave of Rats dies, if it dealt combat damage to a player this turn, return it to the battlefield under its owner's control.

Blitz {4}{B} (If you cast this spell for its blitz cost, it gains haste and "When this creature dies, draw a card." Sacrifice it at the beginning of the next end step.)