Karma

At the beginning of each player's upkeep, Karma deals damage to that player equal to the number of Swamps they control.

Plains

Reprieve

Return target spell to its owner's hand.
Draw a card.

Kormus Bell

All Swamps are 1/1 black creatures that are still lands.

Urborg, Tomb of Yawgmoth

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

Eladamri's Call

Search your library for a creature card, reveal that card, put it into your hand, then shuffle.

Drana and Linvala

Flying, vigilance
Activated abilities of creatures your opponents control can't be activated.
Drana and Linvala has all activated abilities of all creatures your opponents control. You may spend mana as though it were mana of any color to activate those abilities.

Overgrown Tomb

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

Godless Shrine

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

Dark Ritual

Dread Presence

Whenever a Swamp you control enters, choose one —
• You draw a card and you lose 1 life.
• Dread Presence deals 2 damage to any target and you gain 2 life.

Forest

Rites of Flourishing

At the beginning of each player's draw step, that player draws an additional card.
Each player may play an additional land on each of their turns.

Crop Rotation

As an additional cost to cast this spell, sacrifice a land.
Search your library for a land card, put that card onto the battlefield, then shuffle.