Drought

At the beginning of your upkeep, sacrifice Drought unless you pay {W}{W}.
Spells cost an additional "Sacrifice a Swamp" to cast for each black mana symbol in their mana costs.
Activated abilities cost an additional "Sacrifice a Swamp" to activate for each black mana symbol in their activation costs.

Angry Mob

Trample
During your turn, Angry Mob's power and toughness are each equal to 2 plus the number of Swamps your opponents control. During turns other than yours, Angry Mob's power and toughness are each 2.

Crusading Knight

Protection from black
Crusading Knight gets +1/+1 for each Swamp your opponents control.

Yavimaya, Cradle of Growth

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

Worship

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

Rune of Protection: White

{W}: The next time a white source of your choice would deal damage to you this turn, prevent that damage.
Cycling {2} ({2}, Discard this card: Draw a card.)

Karma

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

Urza's Cave

{T}: Add {C}.
{3}, {T}, Sacrifice Urza's Cave: Search your library for a land card, put it onto the battlefield tapped, then shuffle.