Counterspell

Monastery Mentor

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast a noncreature spell, create a 1/1 white Monk creature token with prowess.

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Clever Lumimancer

Magecraft — Whenever you cast or copy an instant or sorcery spell, Clever Lumimancer gets +2/+2 until end of turn.

Eluge, the Shoreless Sea

Eluge's power and toughness are each equal to the number of Islands you control.
Whenever Eluge enters or attacks, put a flood counter on target land. It's an Island in addition to its other types for as long as it has a flood counter on it.
The first instant or sorcery spell you cast each turn costs {U} (or {1}) less to cast for each land you control with a flood counter on it.

Take Up the Shield

Put a +1/+1 counter on target creature. It gains lifelink and indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Baral, Chief of Compliance

Instant and sorcery spells you cast cost {1} less to cast.
Whenever a spell or ability you control counters a spell, you may draw a card. If you do, discard a card.

Shelter

Target creature you control gains protection from the color of your choice until end of turn.
Draw a card.

Prologue to Phyresis

Each opponent gets a poison counter.
Draw a card.

Plains

Mocking Sprite

Flying
Instant and sorcery spells you cast cost {1} less to cast.

Island

Disenchant

Thought Scour

Target player mills two cards.
Draw a card.

Zethi, Arcane Blademaster

Multikicker {W/U}
When Zethi, Arcane Blademaster enters, exile up to X target instant cards from your graveyard, where X is the number of times Zethi was kicked. Put a kick counter on each of them.
Whenever Zethi attacks, copy each exiled card you own with a kick counter on it. You may cast the copies.

Loran's Escape

Target artifact or creature gains hexproof and indestructible until end of turn. Scry 1.

Talrand, Sky Summoner

Whenever you cast an instant or sorcery spell, create a 2/2 blue Drake creature token with flying.

Brainstorm

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

Vega, the Watcher

Flying
Whenever you cast a spell from anywhere other than your hand, draw a card.

Leap

Target creature gains flying until end of turn.
Draw a card.

High Tide

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

Faithful Mending

You gain 2 life, draw two cards, then discard two cards.
Flashback {1}{W}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Murmuring Mystic

Whenever you cast an instant or sorcery spell, create a 1/1 blue Bird Illusion creature token with flying.