Have

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Memory Lapse

Counter target spell. If that spell is countered this way, put it on top of its owner's library instead of into that player's graveyard.

Tome Scour

Island

Don't Have

Psychic Barrier

Counter target creature spell. Its controller loses 1 life.

Mana Leak

Counter target spell unless its controller pays {3}.

Shriekgeist

Flying
Whenever Shriekgeist deals combat damage to a player, that player mills two cards.

Mind Sculpt

Halimar Depths

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

Vapor Snag

Return target creature to its owner's hand. Its controller loses 1 life.

Insectile Aberration

Delver of Secrets

At the beginning of your upkeep, look at the top card of your library. You may reveal that card. If an instant or sorcery card is revealed this way, transform Delver of Secrets.

Delver of Secrets // Insectile Aberration

Spire Golem

Affinity for Islands (This spell costs {1} less to cast for each Island you control.)
Flying

Thought Scour

Target player mills two cards.
Draw a card.

Compelling Argument

Target player mills five cards.
Cycling {U} ({U}, Discard this card: Draw a card.)

Dream Twist

Target player mills three cards.
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Countermand

Counter target spell. Its controller mills four cards.