Merfolk Trickster

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

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.

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.

Entrancing Melody

Gain control of target creature with mana value X.

Exclusion Mage

When Exclusion Mage enters, return target creature an opponent controls to its owner's hand.

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.)

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.

Essence Capture

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

Wizard's Retort

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

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Island

Mist-Cloaked Herald

Warkite Marauder

Flying
Whenever Warkite Marauder attacks, target creature defending player controls loses all abilities and has base power and toughness 0/1 until end of turn.

Tempest Djinn

Flying
Tempest Djinn gets +1/+0 for each basic Island you control.

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.