Crypt Rats

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

Divest

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

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

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

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

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

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

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

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