Have

Marit Lage's Slumber

Whenever Marit Lage's Slumber or another snow permanent you control enters, scry 1.
At the beginning of your upkeep, if you control ten or more snow permanents, sacrifice Marit Lage's Slumber. If you do, create Marit Lage, a legendary 20/20 black Avatar creature token with flying and indestructible.

Frost Augur

{S}, {T}: Look at the top card of your library. If it's a snow card, you may reveal it and put it into your hand. ({S} can be paid with one mana from a snow source.)

Rime Transfusion

Enchant creature
Enchanted creature gets +2/+1 and has "{S}: This creature can't be blocked this turn except by snow creatures." ({S} can be paid with one mana from a snow source.)

On Thin Ice

Enchant snow land you control
When this Aura enters, exile target creature an opponent controls until this Aura leaves the battlefield.

Snow-Covered Forest

Glacial Revelation

Reveal the top six cards of your library. You may put any number of snow permanent cards from among them into your hand. Put the rest into your graveyard.

Blizzard Brawl

Choose target creature you control and target creature you don't control. If you control three or more snow permanents, the creature you control gets +1/+0 and gains indestructible until end of turn. Then those creatures fight each other. (Each deals damage equal to its power to the other.)

Replicating Ring

{T}: Add one mana of any color.
At the beginning of your upkeep, put a night counter on this artifact. Then if it has eight or more night counters on it, remove all of them and create eight colorless snow artifact tokens named Replicated Ring with "{T}: Add one mana of any color."

Snow-Covered Island

Blizzard Specter

Flying
Whenever this creature deals combat damage to a player, choose one —
• That player returns a permanent they control to its owner's hand.
• That player discards a card.

Ice-Fang Coatl

Flash
Flying
When this creature enters, draw a card.
This creature has deathtouch as long as you control at least three other snow permanents.

Skred

Skred deals damage to target creature equal to the number of snow permanents you control.

Counterbalance

Whenever an opponent casts a spell, you may reveal the top card of your library. If you do, counter that spell if it has the same mana value as the revealed card.

Winter's Rest

Enchant creature
When this Aura enters, tap enchanted creature.
As long as you control another snow permanent, enchanted creature doesn't untap during its controller's untap step.

Tribute to the Wild

Each opponent sacrifices an artifact or enchantment of their choice.

Avalanche Caller

{2}: Target snow land you control becomes a 4/4 Elemental creature with hexproof and haste until end of turn. It's still a land. (A creature with hexproof can't be the target of spells or abilities your opponents control.)

Sundering Growth

Destroy target artifact or enchantment, then populate. (Create a token that's a copy of a creature token you control.)

Arcum's Astrolabe

({S} can be paid with one mana from a snow source.)
When this artifact enters, draw a card.
{1}, {T}: Add one mana of any color.

Dead of Winter

All nonsnow creatures get -X/-X until end of turn, where X is the number of snow permanents you control.

Boreal Druid

Icy Blast

Tap X target creatures.
Ferocious — If you control a creature with power 4 or greater, those creatures don't untap during their controllers' next untap steps.

Back to Basics

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

Ohran Frostfang

Attacking creatures you control have deathtouch.
Whenever a creature you control deals combat damage to a player, draw a card.

Abominable Treefolk

Trample
Abominable Treefolk's power and toughness are each equal to the number of snow permanents you control.
When this creature enters, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Iceberg Cancrix

Whenever another snow permanent you control enters, you may have target player mill two cards.