Burglar Rat

When this creature enters, each opponent discards a card.

Drainpipe Vermin

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

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 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.

Typhoid Rats

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

Cling to Dust

Exile target card from a graveyard. If it was a creature card, you gain 3 life. Otherwise, you draw a card.
Escape—{3}{B}, Exile five other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Snow-Covered Swamp

Cremate

Exile target card from a graveyard.
Draw a card.

Rat Colony

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

Crypt Rats

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