When Seekers' Squire enters the battlefield, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

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.)
, Exile Sentinel Totem: Exile all cards from all graveyards.

Exile all attacking creatures target player controls. That player may search their library for that many basic land cards, put those cards onto the battlefield tapped, then shuffle their library.

Whenever a creature you control explores, put a +1/+1 counter on Shadowed Caravel.
Crew 2 (Tap any number of creatures you control with total power 2 or more: This Vehicle becomes an artifact creature until end of turn.)

Shaper Apprentice has flying as long as you control another Merfolk.

: Put a +1/+1 counter on target creature.
, Remove a +1/+1 counter from a creature you control: Draw a card.

Whenever a creature you control becomes the target of a spell or ability an opponent controls, you may draw a card.

Target creature gains indestructible until end of turn. Scry 1. (Damage and effects that say "destroy" don't destroy the creature.)

Flying

Raid — When Shipwreck Looter enters the battlefield, if you attacked this turn, you may draw a card. If you do, discard a card.

, , Sacrifice Shore Keeper: Draw three cards.

Flying
When Siren Lookout enters the battlefield, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

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

Exile target creature you control, then return that card to the battlefield under its owner's control. If a Pirate was exiled this way, draw a card.

: Skittering Heartstopper gains deathtouch until end of turn.

Until end of turn, target creature you control gets +1/+1 and target creature an opponent controls gets -1/-1.

Flying, menace

Flying

Flying
When Skymarch Bloodletter enters the battlefield, target opponent loses 1 life and you gain 1 life.

Slash of Talons deals 2 damage to target attacking or blocking creature.