Tidal Visionary

{T}: Target creature becomes the color of your choice until end of turn.

Fylamarid

Flying
Fylamarid can't be blocked by blue creatures.
{U}: Target creature becomes blue until end of turn.

Hunting Drake

Flying
When Hunting Drake enters, put target red or green creature on top of its owner's library.

Treetop Sentinel

Hibernation

Return all green permanents to their owners' hands.

Sky Diamond

Shifting Sky

As Shifting Sky enters, choose a color.
All nonland permanents are the chosen color.

Aether Gust

Choose target spell or permanent that's red or green. Its owner puts it on their choice of the top or bottom of their library.

Tidebinder Mage

When Tidebinder Mage enters, tap target red or green creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control Tidebinder Mage.

Cerulean Drake

Flying
Protection from red (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything red.)
Sacrifice Cerulean Drake: Counter target spell that targets you.

Hydroblast

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

Heartstone

Activated abilities of creatures cost {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice Mind Stone: Draw a card.

Narwhal

Jace's Defeat

Counter target blue spell. If it was a Jace planeswalker spell, scry 2.

Coast Watcher

Distorting Lens

{T}: Target permanent becomes the color of your choice until end of turn.

Master of Waves

Protection from red
Elemental creatures you control get +1/+1.
When Master of Waves enters, create a number of 1/0 blue Elemental creature tokens equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Wrath of Marit Lage

When Wrath of Marit Lage enters, tap all red creatures.
Red creatures don't untap during their controllers' untap steps.

Wash Out

Return all permanents of the color of your choice to their owners' hands.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Vodalian Mystic

{T}: Target instant or sorcery spell becomes the color of your choice.

Cerulean Wyvern

Blue Elemental Blast

Choose one —
• Counter target red spell.
• Destroy target red permanent.

Blind Seer

{1}{U}: Target spell or permanent becomes the color of your choice until end of turn.

Dreamscape Artist

{2}{U}, {T}, Discard a card, Sacrifice a land: Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

Weatherseed Faeries

Flashfreeze

Jaded Response

Counter target spell if it shares a color with a creature you control.

Inundate

Return all nonblue creatures to their owners' hands.

Gainsay

King Crab

{1}{U}, {T}: Put target green creature on top of its owner's library.

Shell Skulkin

{3}: Target blue creature gains shroud until end of turn. (It can't be the target of spells or abilities.)

Blue Sun's Zenith

Target player draws X cards. Shuffle Blue Sun's Zenith into its owner's library.

Tidal Control

Cumulative upkeep {2} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Pay 2 life or {2}: Counter target red or green spell. Any player may activate this ability.

Flash Flood

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

Sway of Illusion

Any number of target creatures become the color of your choice until end of turn.
Draw a card.

Well-Laid Plans

Prevent all damage that would be dealt to a creature by another creature if they share a color.

Douse

Llawan, Cephalid Empress

When Llawan, Cephalid Empress enters, return all blue creatures your opponents control to their owners' hands.
Your opponents can't cast blue creature spells.

Deepchannel Mentor

Blue creatures you control can't be blocked.

Govern the Guildless

Gain control of target monocolored creature.
Forecast — {1}{U}, Reveal Govern the Guildless from your hand: Target creature becomes the color or colors of your choice until end of turn. (Activate only during your upkeep and only once each turn.)

Sol Ring

Indigo Faerie

Flying
{U}: Target permanent becomes blue in addition to its other colors until end of turn.

Scuttlemutt

{T}: Add one mana of any color.
{T}: Target creature becomes the color or colors of your choice until end of turn.