Windfall

Each player discards their hand, then draws cards equal to the greatest number of cards a player discarded this way.

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."

Blue Elemental Blast

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

Serum Visions

Well-Laid Plans

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

Tidal Visionary

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

Blind Seer

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

Flash Flood

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

Hibernation

Return all green permanents to their owners' hands.

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.

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.

Hydroblast

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

Distorting Lens

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

Douse

Baleful Stare

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

Sword of Once and Future

Equipped creature gets +2/+2 and has protection from blue and from black.
Whenever equipped creature deals combat damage to a player, surveil 2. Then you may cast an instant or sorcery spell with mana value 2 or less from your graveyard without paying its mana cost. If that spell would be put into your graveyard, exile it instead.
Equip {2}

Llawan, Cephalid Empress

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

Wash Out

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

Sway of Illusion

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

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.

High Tide

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

Trait Doctoring

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.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

Sky Diamond

Sky Diamond enters the battlefield tapped.
{T}: Add {U}.

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.)

Mana Maze

Players can't cast spells that share a color with the spell most recently cast this turn.

Arcane Signet

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

Scuttlemutt

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

Shifting Sky

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

High Seas

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

Insight

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

Mind Harness

Enchant red or green creature
Cumulative upkeep {1} (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.)
You control enchanted creature.