Mist-Cloaked Herald

Nightveil Sprite

Flying
Whenever Nightveil Sprite attacks, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Spell Pierce

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

Sleep

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

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.

Disdainful Stroke

Counter target spell with mana value 4 or greater.

Island

Diamond Mare

As Diamond Mare enters the battlefield, choose a color.
Whenever you cast a spell of the chosen color, you gain 1 life.

Merfolk Trickster

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

Wizard's Retort

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

Syncopate

Counter target spell unless its controller pays {X}. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Siren Stormtamer

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

Exclusion Mage

When Exclusion Mage enters the battlefield, 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.)

Sentinel Totem

When Sentinel Totem enters the battlefield, scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)
{T}, Exile Sentinel Totem: Exile all graveyards.

Blink of an Eye

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
Return target nonland permanent to its owner's hand. If this spell was kicked, draw a card.