Blue Elemental Blast

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

Flash Flood

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

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

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.

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.)

Hibernation

Return all green permanents to their owners' hands.

Tidal Visionary

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

Well-Laid Plans

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

Distorting Lens

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

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.

Insight

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

Sway of Illusion

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

Counterspell

Scuttlemutt

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

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.

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.

Douse

Arcane Denial

Counter target spell. Its controller may draw up to two cards at the beginning of the next turn's upkeep.
You draw a card at the beginning of the next turn's upkeep.

Shifting Sky

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

Wash Out

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

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.