Ixalan

Daring Saboteur | Creature | Human Pirate | {2}{U}: Daring Saboteur can't be blocked this turn. Whenever Daring Saboteur deals combat damage to a player, you may draw a card. If you do, discard a card. | Victor Adame Minguez

Dreamcaller Siren | Creature | Siren Pirate | Flash Flying Dreamcaller Siren can block only creatures with flying. When Dreamcaller Siren enters the battlefield, if you control another Pirate, tap up to two target nonland permanents. | Eric Deschamps

Fleet Swallower | Creature | Fish | Whenever Fleet Swallower attacks, target player mills half their library, rounded up. | Tomasz Jedruszek

Herald of Secret Streams | Creature | Merfolk Warrior | Creatures you control with +1/+1 counters on them can't be blocked. | Sara Winters

Kopala, Warden of Waves | Legendary Creature | Merfolk Wizard | Spells your opponents cast that target a Merfolk you control cost {2} more to cast. Abilities your opponents activate that target a Merfolk you control cost {2} more to activate. | Magali Villeneuve

Hostage Taker | Creature | Human Pirate | When Hostage Taker enters the battlefield, exile another target creature or artifact until Hostage Taker leaves the battlefield. You may cast that card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast that spell. | Wayne Reynolds