Rivals of Ixalan

Crashing Tide | Sorcery | | This spell has flash as long as you control a Merfolk. Return target creature to its owner's hand. Draw a card. | Carmen Sinek

River Darter | Creature | Merfolk Warrior | River Darter can't be blocked by Dinosaurs. | Winona Nelson

Sailor of Means | Creature | Human Pirate | When Sailor of Means enters the battlefield, create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.") | Ryan Pancoast

Secrets of the Golden City | Sorcery | | Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.) Draw two cards. If you have the city's blessing, draw three cards instead. | Jason Felix

Waterknot | Enchantment | Aura | Enchant creature When Waterknot enters the battlefield, tap enchanted creature. Enchanted creature doesn't untap during its controller's untap step. | Wayne Reynolds