Dive Down

Target creature you control gets +0/+3 and gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

Essence Capture

Counter target creature spell. Put a +1/+1 counter on up to one target creature you control.

Entrancing Melody

Gain control of target creature with mana value X.

Deep Freeze

Enchant creature
Enchanted creature has base power and toughness 0/4, has defender, loses all other abilities, and is a blue Wall in addition to its other colors and types.

Wizard's Retort

This spell costs {1} less to cast if you control a Wizard.
Counter target spell.

Spell Pierce

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

Siren Stormtamer

Flying
{U}, Sacrifice Siren Stormtamer: Counter target spell or ability that targets you or a creature you control.

Tempest Djinn

Flying
This creature gets +1/+0 for each basic Island you control.

Merfolk Trickster

Flash
When Merfolk Trickster enters, tap target creature an opponent controls. It loses all abilities until end of turn.

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Island

Curious Obsession

Enchant creature
Enchanted creature gets +1/+1 and has "Whenever this creature deals combat damage to a player, you may draw a card."
At the beginning of your end step, if you didn't attack with a creature this turn, sacrifice Curious Obsession.

Jace, Cunning Castaway

+1: Whenever one or more creatures you control deal combat damage to a player this turn, draw a card, then discard a card.
−2: Create a 2/2 blue Illusion creature token with "When this creature becomes the target of a spell, sacrifice it."
−5: Create two tokens that are copies of Jace, Cunning Castaway, except they're not legendary.

Chart a Course

Draw two cards. Then discard a card unless you attacked this turn.

Disdainful Stroke

Counter target spell with mana value 4 or greater.

Mist-Cloaked Herald

Negate

Surge Mare

Surge Mare can't be blocked by green creatures.
Whenever Surge Mare deals damage to an opponent, you may draw a card. If you do, discard a card.
{1}{U}: Surge Mare gets +2/-2 until end of turn.

Pteramander

Flying
{7}{U}: Adapt 4. This ability costs {1} less to activate for each instant and sorcery card in your graveyard. (If this creature has no +1/+1 counters on it, put four +1/+1 counters on it.)