Reckoner's Bargain

As an additional cost to cast this spell, sacrifice an artifact or creature.
You gain life equal to the sacrificed permanent's mana value. Draw two cards.

Spread the Sickness

Destroy target creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Ossuary Rats

When Ossuary Rats enters the battlefield, it deals X damage to target creature or planeswalker an opponent controls, where X is the number of creature cards in your graveyard.

Study Hall

{T}: Add {C}.
{1}, {T}: Add one mana of any color. When you spend this mana to cast your commander, scry X, where X is the number of times it's been cast from the command zone this game.

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.)

You Are Already Dead

Destroy target creature that was dealt damage this turn.
Draw a card.

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.

Forever Young

Put any number of target creature cards from your graveyard on top of your library.
Draw a card.

Graf Rats

At the beginning of combat on your turn, if you both own and control Graf Rats and a creature named Midnight Scavengers, exile them, then meld them into Chittering Host.

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.)

Barren Moor

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

Biblioplex Assistant

Flying
When Biblioplex Assistant enters the battlefield, put up to one target instant or sorcery card from your graveyard on top of your library.

Forge of Heroes

{T}: Add {C}.
{T}: Choose target commander that entered the battlefield this turn. Put a +1/+1 counter on it if it's a creature and a loyalty counter on it if it's a planeswalker.

Rats' Feast

Exile X target cards from a single graveyard.

Swamp

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."

Witch's Cottage

({T}: Add {B}.)
Witch's Cottage enters the battlefield tapped unless you control three or more other Swamps.
When Witch's Cottage enters the battlefield untapped, you may put target creature card from your graveyard on top of your library.

Sign in Blood

Target player draws two cards and loses 2 life.

Fanatical Offering

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards and create a Map token. (It's an artifact with "{1}, {T}, Sacrifice this artifact: Target creature you control explores. Activate only as a sorcery.")

Voracious Vermin

When Voracious Vermin enters the battlefield, create a 1/1 black Rat creature token with "This creature can't block."
Whenever another creature you control dies, put a +1/+1 counter on Voracious Vermin.

Piranha Marsh

Piranha Marsh enters the battlefield tapped.
When Piranha Marsh enters the battlefield, target player loses 1 life.
{T}: Add {B}.

Mirrodin Avenged

Polluted Mire

Polluted Mire enters the battlefield tapped.
{T}: Add {B}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Corrupted Conviction

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

Path of Ancestry

Path of Ancestry enters the battlefield tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Village Rites

Swarm of Rats

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

Mortuary Mire

Mortuary Mire enters the battlefield tapped.
When Mortuary Mire enters the battlefield, you may put target creature card from your graveyard on top of your library.
{T}: Add {B}.

Midnight Scavengers

When Midnight Scavengers enters the battlefield, you may return target creature card with mana value 3 or less from your graveyard to your hand.
(Melds with Graf Rats.)

Footbottom Feast

Desert of the Glorified

Desert of the Glorified enters the battlefield tapped.
{T}: Add {B}.
Cycling {1}{B} ({1}{B}, Discard this card: Draw a card.)

The Dross Pits

The Dross Pits enters the battlefield tapped.
{T}: Add {B}.
{1}{B}, {T}, Sacrifice The Dross Pits: Draw a card.

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.)