Smallpox

Each player loses 1 life, discards a card, sacrifices a creature of their choice, then sacrifices a land of their choice.

Pack Rat

Pack Rat's power and toughness are each equal to the number of Rats you control.
{2}{B}, Discard a card: Create a token that's a copy of Pack Rat.

Burglar Rat

When Burglar Rat enters, each opponent discards a card.

Drainpipe Vermin

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

Call to the Netherworld

Return target black creature card from your graveyard to your hand.
Madness {0} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Waste Not

Whenever an opponent discards a creature card, create a 2/2 black Zombie creature token.
Whenever an opponent discards a land card, add {B}{B}.
Whenever an opponent discards a noncreature, nonland card, draw a card.

Swarmyard

{T}: Add {C}.
{T}: Regenerate target Insect, Rat, Spider, or Squirrel. (The next time it would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Distress

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

Dark Ritual

Typhoid Rats

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

Duress

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

Swamp

Murderous Cut

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Destroy target creature.

Rotting Rats

When Rotting Rats enters, each player discards a card.
Unearth {1}{B} ({1}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)