Typhoid Rats

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

Ravenous Rats

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

Doom Blade

Duress

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

Go for the Throat

Chittering Rats

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

Bad Moon

Burglar Rat

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

Piper of the Swarm

Rats you control have menace.
{1}{B}, {T}: Create a 1/1 black Rat creature token.
{2}{B}{B}, {T}, Sacrifice three Rats: Gain control of target creature.

Ruin Rat

Deathtouch
When Ruin Rat dies, exile target card from an opponent's graveyard.

Okiba-Gang Shinobi

Ninjutsu {3}{B} ({3}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Okiba-Gang Shinobi deals combat damage to a player, that player discards two cards.