Defile

Target creature gets -1/-1 until end of turn for each Swamp you control.

Bubbling Muck

Until end of turn, whenever a player taps a Swamp for mana, that player adds an additional {B}.

Meekstone

Creatures with power 3 or greater don't untap during their controllers' untap steps.

Iron Maiden

At the beginning of each opponent's upkeep, Iron Maiden deals X damage to that player, where X is the number of cards in their hand minus 4.

Urborg, Tomb of Yawgmoth

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

Sheoldred, Whispering One

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
At the beginning of your upkeep, return target creature card from your graveyard to the battlefield.
At the beginning of each opponent's upkeep, that player sacrifices a creature of their choice.

Swift Reconfiguration

Flash
Enchant creature or Vehicle
Enchanted permanent is a Vehicle artifact with crew 5 and it loses all other card types. (It's not a creature unless it's crewed.)

Greasefang, Okiba Boss

At the beginning of combat on your turn, return target Vehicle card from your graveyard to the battlefield. It gains haste. Return it to its owner's hand at the beginning of your next end step.

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.

Mutilate

All creatures get -1/-1 until end of turn for each Swamp you control.

Consume the Meek

Destroy each creature with mana value 3 or less. They can't be regenerated.

Lost Soul

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)

Retribution of the Meek

Destroy all creatures with power 4 or greater. They can't be regenerated.

Smokestack

At the beginning of your upkeep, you may put a soot counter on Smokestack.
At the beginning of each player's upkeep, that player sacrifices a permanent of their choice for each soot counter on Smokestack.

Quag Sickness

Enchant creature
Enchanted creature gets -1/-1 for each Swamp you control.

Worship

If you control a creature, damage that would reduce your life total to less than 1 reduces it to 1 instead.