Drainpipe Vermin

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

Go for the Throat

Ravenous Rats

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

Nezumi Bone-Reader

{B}, Sacrifice a creature: Target player discards a card. Activate only as a sorcery.

Tragic Slip

Target creature gets -1/-1 until end of turn.
Morbid — That creature gets -13/-13 until end of turn instead if a creature died this turn.

Duress

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

Mind Rot

Distress

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

Ratcatcher

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
At the beginning of your upkeep, you may search your library for a Rat card, reveal it, put it into your hand, then shuffle.

Sign in Blood

Target player draws two cards and loses 2 life.

Swamp

Despise

Target opponent reveals their hand. You choose a creature or planeswalker card from it. That player discards that card.

Altar's Reap

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

Marrow-Gnawer

All Rats have fear.
{T}, Sacrifice a Rat: Create X 1/1 black Rat creature tokens, where X is the number of Rats you control.

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.