Burglar Rat

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

Ravenous Rats

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

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

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

Plague Rats's power and toughness are each equal to the number of creatures named Plague Rats on the battlefield.

{B}, Pay 1 life: Sewer Rats gets +1/+0 until end of turn. Activate no more than three times each turn.

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

Target player sacrifices a creature.
Flashback {5}{B}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

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

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

Target player reveals their hand. You choose an artifact or creature card from it. That player discards that card.