Voracious Vermin

When Voracious Vermin enters, create a 1/1 black Rat creature token with "This creature can't block."
Whenever another creature you control dies, put a +1/+1 counter on Voracious Vermin.

Cursed

Enchant creature
Enchanted creature has base power and toughness 1/1.

Wicked

Enchant creature
Enchanted creature gets +1/+1.
When this Aura is put into a graveyard from the battlefield, each opponent loses 1 life.

Wicked // Cursed

Gnawing Crescendo

Creatures you control get +2/+0 until end of turn. Whenever a nontoken creature you control dies this turn, create a 1/1 black Rat creature token with "This creature can't block."

Twisted Sewer-Witch

When Twisted Sewer-Witch enters, create a 1/1 black Rat creature token with "This creature can't block." Then for each Rat you control, create a Wicked Role token attached to that Rat. (If you control another Role on it, put that one into the graveyard. Enchanted creature gets +1/+1. When this Aura is put into a graveyard, each opponent loses 1 life.)

Totentanz, Swarm Piper

Whenever Totentanz, Swarm Piper or another nontoken creature you control dies, create a 1/1 black Rat creature token with "This creature can't block."
{1}{B}: Target attacking Rat you control gains deathtouch until end of turn.

Mountain

Jagged Barrens

Jagged Barrens enters tapped.
When Jagged Barrens enters, it deals 1 damage to target opponent.
{T}: Add {B} or {R}.

Corrupted Conviction

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

Lord Skitter's Butcher

When Lord Skitter's Butcher enters, choose one —
• Create a 1/1 black Rat creature token with "This creature can't block."
• You may sacrifice another creature. If you do, scry 2, then draw a card.
• Creatures you control gain menace until end of turn.

Tattered Ratter

Whenever a Rat you control becomes blocked, it gets +2/+0 until end of turn.

Pest Problem

Create two 1/1 black Rat creature tokens with "This creature can't block." (Then exile this card. You may cast the creature later from exile.)

Ratcatcher Trainee

During your turn, Ratcatcher Trainee has first strike.

Ratcatcher Trainee // Pest Problem

Dogpile

Dogpile deals damage to any target equal to the number of attacking creatures you control.

Rat Out

Up to one target creature gets -1/-1 until end of turn. You create a 1/1 black Rat creature token with "This creature can't block."

Edgewall Pack

Menace (This creature can't be blocked except by two or more creatures.)
When Edgewall Pack enters, create a 1/1 black Rat creature token with "This creature can't block."

Swamp

Song of Totentanz

Create X 1/1 black Rat creature tokens with "This creature can't block." Creatures you control gain haste until end of turn.

Harried Spearguard

Haste
When Harried Spearguard dies, create a 1/1 black Rat creature token with "This creature can't block."