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.

Baleful Stare

Target opponent reveals their hand. You draw a card for each Mountain and red card in it.

Shifting Sky

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

Chameleon Spirit

As Chameleon Spirit enters, choose a color.
Chameleon Spirit's power and toughness are each equal to the number of permanents of the chosen color your opponents control.

Well-Laid Plans

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

Arcanis the Omnipotent

{T}: Draw three cards.
{2}{U}{U}: Return Arcanis to its owner's hand.

Island

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Spellbook

Fylamarid

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

Prismatic Lace

Target permanent becomes the color or colors of your choice. (This effect lasts indefinitely.)

Insight

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

Gainsay

Hydroblast

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

Mystical Tutor

Search your library for an instant or sorcery card, reveal it, then shuffle and put that card on top.

Hibernation

Return all green permanents to their owners' hands.

Grindstone

{3}, {T}: Target player mills two cards. If two cards that share a color were milled this way, repeat this process.

Sway of Illusion

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

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.

Blind Seer

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

Blue Elemental Blast

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

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

Metathran Transport

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

Sleight of Mind

Change the text of target spell or permanent by replacing all instances of one color word with another. (For example, you may change "target black spell" to "target blue spell." This effect lasts indefinitely.)

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Counterspell

Whim of Volrath

Buyback {2} (You may pay an additional {2} as you cast this spell. If you do, put this card into your hand as it resolves.)
Change the text of target permanent by replacing all instances of one color word with another or one basic land type with another until end of turn. (For example, you may change "nonred creature" to "nongreen creature" or "plainswalk" to "swampwalk.")

King Crab

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

Distorting Lens

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

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.

Cowardice

Whenever a creature becomes the target of a spell or ability, return that creature to its owner's hand. (It won't be affected by the spell or ability.)

Sol Ring

Alter Reality

Change the text of target spell or permanent by replacing all instances of one color word with another. (This effect lasts indefinitely.)
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Douse

Sea Kings' Blessing

One or more target creatures become blue until end of turn.

Jaded Response

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

Mana Drain

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

Riptide

Merchant Scroll

Search your library for a blue instant card, reveal that card, put it into your hand, then shuffle.

Wash Out

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

Force of Will

You may pay 1 life and exile a blue card from your hand rather than pay this spell's mana cost.
Counter target spell.

Withering Gaze

Target opponent reveals their hand. You draw a card for each Forest and green card in it.

Crystal Spray

Change the text of target spell or permanent by replacing all instances of one color word with another or one basic land type with another until end of turn.
Draw a card.

Vodalian Mystic

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

Tidal Visionary

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

Ether Well

Put target creature on top of its owner's library. If that creature is red, you may put it on the bottom of its owner's library instead.

Flash Flood

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

Barrin's Unmaking

Return target permanent to its owner's hand if that permanent shares a color with the most common color among all permanents or a color tied for most common.