Duress

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

Ravenous Rats

When this creature enters, target opponent discards a card.

Burglar Rat

When this creature enters, each opponent discards a card.

Gnat Miser

Each opponent's maximum hand size is reduced by one.

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 this creature deals combat damage to a player, that player discards two cards.

Typhoid Rats

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