Brinebarrow Intruder

Flash
When this creature enters, target creature an opponent controls gets -2/-0 until end of turn.

Protocol Knight

When this creature enters, tap target creature an opponent controls. Put a stun counter on that creature if you control another Knight. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Sage's Row Denizen

Whenever another blue creature you control enters, target player mills two cards.

Archaeomancer

When this creature enters, return target instant or sorcery card from your graveyard to your hand.

Unsummon

Return target creature to its owner's hand.

Augury Owl

Flying
When this creature enters, scry 3. (Look at the top three cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Tome Raider

Flying
When this creature enters, draw a card.

Counterspell

Preening Champion

Flying
When this creature enters, create a 1/1 blue and red Elemental creature token.

Island

Illusionist's Stratagem

Exile up to two target creatures you control, then return those cards to the battlefield under their owner's control.
Draw a card.

Thriving Isle

This land enters tapped. As it enters, choose a color other than blue.
{T}: Add {U} or one mana of the chosen color.

Conjurer's Closet

At the beginning of your end step, you may exile target creature you control, then return that card to the battlefield under your control.

Thassa, Deep-Dwelling

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature.
At the beginning of your end step, exile up to one other target creature you control, then return that card to the battlefield under your control.
{3}{U}: Tap another target creature.

Aether Channeler

When this creature enters, choose one —
• Create a 1/1 white Bird creature token with flying.
• Return another target nonland permanent to its owner's hand.
• Draw a card.

Cryptic Spires

As you create your deck, circle two of the colors below.
This land enters tapped.
{T}: Add one mana of either of the circled colors.