Briarberry Cohort

Flying
Briarberry Cohort gets +1/+1 as long as you control another blue creature.

Faerie Duelist

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

Snaremaster Sprite

Flying
When Snaremaster Sprite enters, you may pay {2}. When you do, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Island

Doom Blade

Terror

Destroy target nonartifact, nonblack creature. It can't be regenerated.

Sea Sprite

Cast Down

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Mocking Sprite

Flying
Instant and sorcery spells you cast cost {1} less to cast.

Counterspell

Faerie Seer

Flying
When Faerie Seer enters, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)