Sideboard

Negate

Don't Have

Nightveil Sprite

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

Tempest Djinn

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

Island

Merfolk Trickster

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

Diamond Mare

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

Sentinel Totem

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

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.

Sleep

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

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}.

Exclusion Mage

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

Disdainful Stroke

Counter target spell with mana value 4 or greater.

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.

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.

Siren Stormtamer

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

Mist-Cloaked Herald

Essence Scatter

Chart a Course

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

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.)