Chittering Rats

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

Pestilence Rats

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.)

Thermo-Alchemist

Defender
{T}: Thermo-Alchemist deals 1 damage to each opponent.
Whenever you cast an instant or sorcery spell, untap Thermo-Alchemist.

Night's Whisper

Bojuka Bog

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

Typhoid Rats

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

Echoing Return

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

Defile

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

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters the battlefield, 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.)

Mountain

Sugar Rush

Target creature gets +3/+0 until end of turn.
Draw a card.

Tormod's Crypt

{T}, Sacrifice Tormod's Crypt: Exile target player's graveyard.

Cast Down

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.)

Sign in Blood

Target player draws two cards and loses 2 life.

Crypt Rats

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

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Dark Ritual

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Read the Bones

Scry 2, then draw two cards. You lose 2 life.

Faithless Looting

Draw two cards, then discard two cards.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Rat Colony

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

Ravenous Rats

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

Serrated Scorpion

When Serrated Scorpion dies, it deals 2 damage to each opponent and you gain 2 life.

Cosmotronic Wave

Cosmotronic Wave deals 1 damage to each creature your opponents control. Creatures your opponents control can't block this turn.

Rat Out

Up to one target creature gets -1/-1 until end of turn. You create a 1/1 black Rat creature token with "This creature can't block."

Relentless Rats

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.

Disfigure

Target creature gets -2/-2 until end of turn.

Warlord's Fury

Creatures you control gain first strike until end of turn.
Draw a card.

Barren Moor

Barren Moor enters the battlefield tapped.
{T}: Add {B}.
Cycling {B} ({B}, Discard this card: Draw a card.)

Echoing Decay

Target creature and all other creatures with the same name as that creature get -2/-2 until end of turn.

Crash Through

Creatures you control gain trample until end of turn. (A creature with trample can deal excess combat damage to the player or planeswalker it's attacking.)
Draw a card.

Swamp

Bloodfell Caves

Bloodfell Caves enters the battlefield tapped.
When Bloodfell Caves enters the battlefield, you gain 1 life.
{T}: Add {B} or {R}.