Counterspell

Hedron Crab

Landfall — Whenever a land you control enters, target player mills three cards. (They put the top three cards of their library into their graveyard.)

Manic Scribe

When this creature enters, each opponent mills three cards.
Delirium — At the beginning of each opponent's upkeep, if there are four or more card types among cards in your graveyard, that player mills three cards.

Flare of Denial

You may sacrifice a nontoken blue creature rather than pay this spell's mana cost.
Counter target spell.

Maddening Cacophony

Kicker {3}{U}
Each opponent mills eight cards. If this spell was kicked, instead each opponent mills half their library, rounded up.

Fractured Sanity

Each opponent mills fourteen cards.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)
When you cycle this card, each opponent mills four cards.

Tasha's Hideous Laughter

Each opponent exiles cards from the top of their library until that player has exiled cards with total mana value 20 or greater.

The Bath Song

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I, II — Draw two cards, then discard a card.
III — Shuffle any number of target cards from your graveyard into your library. Add {U}{U}.

Force of Negation

If it's not your turn, you may exile a blue card from your hand rather than pay this spell's mana cost.
Counter target noncreature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Archive Trap

If an opponent searched their library this turn, you may pay {0} rather than pay this spell's mana cost.
Target opponent mills thirteen cards.

Wishing Well

{T}: Put a coin counter on this artifact. When you do, you may cast target instant or sorcery card with mana value equal to the number of coin counters on this artifact from your graveyard without paying its mana cost. If that spell would be put into your graveyard, exile it instead. Activate only as a sorcery.

Oboro, Palace in the Clouds

{T}: Add {U}.
{1}: Return Oboro to its owner's hand.

Island

Mitotic Manipulation

Look at the top seven cards of your library. You may put one of those cards onto the battlefield if it has the same name as a permanent. Put the rest on the bottom of your library in any order.

Halimar Depths

This land enters tapped.
When this land enters, look at the top three cards of your library, then put them back in any order.
{T}: Add {U}.

Kitsa, Otterball Elite

Vigilance
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
{T}: Draw a card, then discard a card.
{2}, {T}: Copy target instant or sorcery spell you control. You may choose new targets for the copy. Activate only if Kitsa's power is 3 or greater.

Dimir Aqueduct

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {U}{B}.

Skyline Cascade

This land enters tapped.
When this land enters, target creature an opponent controls doesn't untap during its controller's next untap step.
{T}: Add {U}.

Azorius Chancery

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {W}{U}.

Ruin Crab

Landfall — Whenever a land you control enters, each opponent mills three cards. (To mill a card, a player puts the top card of their library into their graveyard.)

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.