Filth

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
As long as Filth is in your graveyard and you control a Swamp, creatures you control have swampwalk.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Urborg, Tomb of Yawgmoth

Each land is a Swamp in addition to its other land types.

Faithless Looting

Draw two cards, then discard two cards.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Blackcleave Cliffs

Blackcleave Cliffs enters tapped unless you control two or fewer other lands.
{T}: Add {B} or {R}.

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.

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.

Mountain

Alesha, Who Smiles at Death

First strike
Whenever Alesha, Who Smiles at Death attacks, you may pay {W/B}{W/B}. If you do, return target creature card with power 2 or less from your graveyard to the battlefield tapped and attacking.

Thoughtseize

Target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Swamp

Rat Colony

Rat Colony gets +1/+0 for each other Rat you control.
A deck can have any number of cards named Rat Colony.

Lightning Axe

As an additional cost to cast this spell, discard a card or pay {5}.
Lightning Axe deals 5 damage to target creature.

Swarmyard

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

Blood Crypt

({T}: Add {B} or {R}.)
As Blood Crypt enters, you may pay 2 life. If you don't, it enters tapped.