Waterknot

Enchant creature
When Waterknot enters the battlefield, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Roil Elemental

Flying
Landfall — Whenever a land enters the battlefield under your control, you may gain control of target creature for as long as you control Roil Elemental.

High Seas

Red creature spells and green creature spells cost {1} more to cast.

Deep Freeze

Enchant creature
Enchanted creature has base power and toughness 0/4, has defender, loses all other abilities, and is a blue Wall in addition to its other colors and types.

Hydrosurge

Target creature gets -5/-0 until end of turn.

Waterwhirl

Return up to two target creatures to their owners' hands.

Ray of Frost

Flash
Enchant creature
When Ray of Frost enters the battlefield, if enchanted creature is red, tap it.
As long as enchanted creature is red, it loses all abilities.
Enchanted creature doesn't untap during its controller's untap step.

Aquamoeba

Discard a card: Switch Aquamoeba's power and toughness until end of turn.

Flashfreeze

Frost Breath

Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.

Glacial Grasp

Tap target creature. Its controller mills two cards. That creature doesn't untap during its controller's next untap step. (They put the top two cards of their library into their graveyard.)
Draw a card.

Engulf the Shore

Return to their owners' hands all creatures with toughness less than or equal to the number of Islands you control.

Living Tsunami

Flying
At the beginning of your upkeep, sacrifice Living Tsunami unless you return a land you control to its owner's hand.

Chilling Trap

Target creature gets -4/-0 until end of turn. If you control a Wizard, draw a card.

Flood of Tears

Return all nonland permanents to their owners' hands. If you return four or more nontoken permanents you control this way, you may put a permanent card from your hand onto the battlefield.

Early Frost

Glacial Wall

Frost Walker

When Frost Walker becomes the target of a spell or ability, sacrifice it.

Waterspout Elemental

Kicker {U} (You may pay an additional {U} as you cast this spell.)
Flying
When Waterspout Elemental enters the battlefield, if it was kicked, return all other creatures to their owners' hands and you skip your next turn.

Flash Flood

Choose one —
• Destroy target red permanent.
• Return target Mountain to its owner's hand.

Iceberg Cancrix

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

Yarok's Wavecrasher

When Yarok's Wavecrasher enters the battlefield, return another creature you control to its owner's hand.

Ominous Seas

Whenever you draw a card, put a foreshadow counter on Ominous Seas.
Remove eight foreshadow counters from Ominous Seas: Create an 8/8 blue Kraken creature token.
Cycling {2} ({2}, Discard this card: Draw a card.)

Remote Isle

Remote Isle enters the battlefield tapped.
{T}: Add {U}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Hydrolash

Attacking creatures get -2/-0 until end of turn.
Draw a card.

Frost Lynx

When Frost Lynx enters the battlefield, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Tidal Force

At the beginning of each upkeep, you may tap or untap target permanent.

Soul of the Rapids

Flying
Hexproof (This creature can't be the target of spells or abilities your opponents control.)

Frozen Solid

Enchant creature
Enchanted creature doesn't untap during its controller's untap step.
When enchanted creature is dealt damage, destroy it.

Thawing Glaciers

Thawing Glaciers enters the battlefield tapped.
{1}, {T}: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle. Return Thawing Glaciers to its owner's hand at the beginning of the next cleanup step.

Dark Depths

Dark Depths enters the battlefield with ten ice counters on it.
{3}: Remove an ice counter from Dark Depths.
When Dark Depths has no ice counters on it, sacrifice it. If you do, create Marit Lage, a legendary 20/20 black Avatar creature token with flying and indestructible.

Rain of Revelation

Brain Freeze

Target player mills three cards.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Brackwater Elemental

When Brackwater Elemental attacks or blocks, sacrifice it at the beginning of the next end step.
Unearth {2}{U} ({2}{U}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Water Servant

{U}: Water Servant gets +1/-1 until end of turn.
{U}: Water Servant gets -1/+1 until end of turn.

Brine Elemental

Morph {5}{U}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Brine Elemental is turned face up, each opponent skips their next untap step.

Glacial Crasher

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Glacial Crasher can't attack unless there is a Mountain on the battlefield.

Uncomfortable Chill

Creatures your opponents control get -2/-0 until end of turn.
Draw a card.

Ice Cave

Whenever a player casts a spell, any other player may pay that spell's mana cost. If a player does, counter the spell. (Mana cost includes color.)

Roiling Waters

Return up to two target creatures your opponents control to their owners' hands. Target player draws two cards.

Watercourser

{U}: Watercourser gets +1/-1 until end of turn.

Tidespout Tyrant

Flying
Whenever you cast a spell, return target permanent to its owner's hand.

Boreal Elemental

Flying
Spells your opponents cast that target Boreal Elemental cost {2} more to cast.

Wave-Wing Elemental

Flying
Landfall — Whenever a land enters the battlefield under your control, Wave-Wing Elemental gets +2/+2 until end of turn.

Shorecrasher Elemental

{U}: Exile Shorecrasher Elemental, then return it to the battlefield face down under its owner's control.
{1}: Shorecrasher Elemental gets +1/-1 or -1/+1 until end of turn.
Megamorph {4}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)

Wall of Frost

Defender
Whenever Wall of Frost blocks a creature, that creature doesn't untap during its controller's next untap step.

Rising Waters

Lands don't untap during their controllers' untap steps.
At the beginning of each player's upkeep, that player untaps a land they control.

Chronic Flooding

Enchant land
Whenever enchanted land becomes tapped, its controller mills three cards.

Octavia, Living Thesis

This spell costs {8} less to cast if you have eight or more instant and/or sorcery cards in your graveyard.
Ward {8}
Magecraft — Whenever you cast or copy an instant or sorcery spell, target creature has base power and toughness 8/8 until end of turn.

Icebind Pillar

{S}, {T}: Tap target artifact or creature. ({S} can be paid with one mana from a snow source.)

Floodhound

{3}, {T}: Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Scion of Glaciers

{U}: Scion of Glaciers gets +1/-1 until end of turn.

Cone of Cold

Roll a d20.
1—9 | Tap all creatures your opponents control.
10—19 | Tap all creatures your opponents control. Those creatures don't untap during their controllers' next untap steps.
20 | Tap all creatures your opponents control. Those creatures don't untap during their controllers' next untap steps. Until your next turn, creatures your opponents control enter the battlefield tapped.

Winter's Chill

Cast this spell only during combat before blockers are declared.
X can't be greater than the number of snow lands you control.
Choose X target attacking creatures. For each of those creatures, its controller may pay {1} or {2}. If that player doesn't, destroy that creature at end of combat. If that player pays only {1}, prevent all combat damage that would be dealt to and dealt by that creature this combat.

Flood

{U}{U}: Tap target creature without flying.

Halimar Depths

Halimar Depths enters the battlefield tapped.
When Halimar Depths enters the battlefield, look at the top three cards of your library, then put them back in any order.
{T}: Add {U}.

Floodwaters

Return up to two target creatures to their owners' hands.
Cycling {2} ({2}, Discard this card: Draw a card.)

Snow-Covered Island

Rush of Ice

Tap target creature. It doesn't untap during its controller's next untap step.
Awaken 3—{4}{U} (If you cast this spell for {4}{U}, also put three +1/+1 counters on target land you control and it becomes a 0/0 Elemental creature with haste. It's still a land.)

Permafrost Trap

If an opponent had a green creature enter the battlefield under their control this turn, you may pay {U} rather than pay this spell's mana cost.
Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.

Tidewalker

Tidewalker enters the battlefield with a time counter on it for each Island you control.
Vanishing (At the beginning of your upkeep, remove a time counter from this creature. When the last is removed, sacrifice it.)
Tidewalker's power and toughness are each equal to the number of time counters on it.

Hydroblast

Choose one —
• Counter target spell if it's red.
• Destroy target permanent if it's red.

Tideforce Elemental

{U}, {T}: You may tap or untap another target creature.
Landfall — Whenever a land enters the battlefield under your control, you may untap Tideforce Elemental.

Water Elemental

Blizzard Elemental

Flooded Shoreline

{U}{U}, Return two Islands you control to their owner's hand: Return target creature to its owner's hand.

Whelming Wave

Return all creatures to their owners' hands except for Krakens, Leviathans, Octopuses, and Serpents.

Chillbringer

Flying
When Chillbringer enters the battlefield, tap target creature an opponent controls. It doesn't untap during its controller's next untap step.

Chill

Whitewater Naiads

Constellation — Whenever Whitewater Naiads or another enchantment enters the battlefield under your control, target creature can't be blocked this turn.

Wall of Water

Defender (This creature can't attack.)
{U}: Wall of Water gets +1/+0 until end of turn.

Clearwater Goblet

Sunburst (This enters the battlefield with a charge counter on it for each color of mana spent to cast it.)
At the beginning of your upkeep, you may gain life equal to the number of charge counters on Clearwater Goblet.