Blind Seer

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

Hydroblast

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

Blue Elemental Blast

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

King Crab

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

Fylamarid

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

Guile

Guile can't be blocked except by three or more creatures.
If a spell or ability you control would counter a spell, instead exile that spell and you may play that card without paying its mana cost.
When Guile is put into a graveyard from anywhere, shuffle it into its owner's library.

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.

Willbreaker

Whenever a creature an opponent controls becomes the target of a spell or ability you control, gain control of that creature for as long as you control Willbreaker.

Homarid Shaman

Treetop Sentinel

Weatherseed Faeries

Coast Watcher

Sea Sprite

Vodalian Mystic

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

Hunting Drake

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

Metathran Transport

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

Douse

Insight

Whenever an opponent casts a green spell, you draw a card.

Dismiss into Dream

Each creature your opponents control is an Illusion in addition to its other types and has "When this creature becomes the target of a spell or ability, sacrifice it."

Shifting Sky

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

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.

Jaded Response

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

Hibernation

Return all green permanents to their owners' hands.

Jace's Defeat

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

Flashfreeze

Flash Flood

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

Gainsay

Aether Gust

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