Snow-Covered Swamp

Jeweled Amulet

{1}, {T}: Put a charge counter on Jeweled Amulet. Note the type of mana spent to pay this activation cost. Activate only if there are no charge counters on Jeweled Amulet.
{T}, Remove a charge counter from Jeweled Amulet: Add one mana of Jeweled Amulet's last noted type.

Each player loses a third of their life, then discards a third of the cards in their hand, then sacrifices a third of the creatures they control of their choice, then sacrifices a third of the lands they control of their choice. Round up each time.

Rancid Earth

Destroy target land.
Threshold — If seven or more cards are in your graveyard, instead destroy that land and Rancid Earth deals 1 damage to each creature and each player.

Sinkhole

Nightscape Battlemage

Kicker {2}{U} and/or {2}{R} (You may pay an additional {2}{U} and/or {2}{R} as you cast this spell.)
When Nightscape Battlemage enters, if it was kicked with its {2}{U} kicker, return up to two target nonblack creatures to their owners' hands.
When Nightscape Battlemage enters, if it was kicked with its {2}{R} kicker, destroy target land.

Smallpox

Each player loses 1 life, discards a card, sacrifices a creature of their choice, then sacrifices a land of their choice.

Icequake

Destroy target land. If that land was a snow land, Icequake deals 1 damage to that land's controller.

Keldon Firebombers

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