Confounding Conundrum

When Confounding Conundrum enters, draw a card.
Whenever a land enters under an opponent's control, if that player had another land enter the battlefield under their control this turn, they return a land they control to its owner's hand.

Magus of the Moon

Impending Disaster

At the beginning of your upkeep, if there are seven or more lands on the battlefield, sacrifice Impending Disaster and destroy all lands.

Catastrophe

Destroy all lands or all creatures. Creatures destroyed this way can't be regenerated.

Blood Moon

Hall of Gemstone

At the beginning of each player's upkeep, that player chooses a color. Until end of turn, lands tapped for mana produce mana of the chosen color instead of any other color.

Overburden

Whenever a player puts a nontoken creature onto the battlefield, that player returns a land they control to its owner's hand.

Mana Breach

Whenever a player casts a spell, that player returns a land they control to its owner's hand.

Tainted Aether

Whenever a creature enters, its controller sacrifices a creature or land.

Back to Basics

Nonbasic lands don't untap during their controllers' untap steps.

Armageddon

Sunder

Winter Moon

Players can't untap more than one nonbasic land during their untap steps.

Storm Cauldron

Each player may play an additional land during each of their turns.
Whenever a land is tapped for mana, return it to its owner's hand.

Winter Orb

As long as Winter Orb is untapped, players can't untap more than one land during their untap steps.

Global Ruin

Each player chooses from the lands they control a land of each basic land type, then sacrifices the rest.

Jegantha, the Wellspring

Companion — No card in your starting deck has more than one of the same mana symbol in its mana cost. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
{T}: Add {W}{U}{B}{R}{G}. This mana can't be spent to pay generic mana costs.

Ravages of War

Desolation

At the beginning of each end step, each player who tapped a land for mana this turn sacrifices a land. Desolation deals 2 damage to each player who sacrificed a Plains this way.

Mana Vortex

When you cast this spell, counter it unless you sacrifice a land.
At the beginning of each player's upkeep, that player sacrifices a land.
When there are no lands on the battlefield, sacrifice Mana Vortex.

Keldon Firebombers

When Keldon Firebombers enters, each player sacrifices all lands they control except for three.

Lavinia, Azorius Renegade

Each opponent can't cast noncreature spells with mana value greater than the number of lands that player controls.
Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell.

Bust

Boom

Destroy target land you control and target land you don't control.

Boom // Bust

Aura of Silence

Artifact and enchantment spells your opponents cast cost {2} more to cast.
Sacrifice Aura of Silence: Destroy target artifact or enchantment.

Ethersworn Canonist

Each player who has cast a nonartifact spell this turn can't cast additional nonartifact spells.

Quicksilver Fountain

At the beginning of each player's upkeep, that player puts a flood counter on target non-Island land they control of their choice. That land is an Island for as long as it has a flood counter on it.
At the beginning of each end step, if all lands on the battlefield are Islands, remove all flood counters from them.