The Lost Caverns of Ixalan

Council of Echoes | Creature | Spirit Advisor | Flying Descend 4 — When Council of Echoes enters the battlefield, if there are four or more permanent cards in your graveyard, return up to one target nonland permanent other than Council of Echoes to its owner's hand. | Fariba Khamseh

Hermitic Nautilus | Artifact Creature | Nautilus | Vigilance {1}{U}: Hermitic Nautilus gets +3/-3 until end of turn. | Logan Feliciano

Merfolk Cave-Diver | Creature | Merfolk Scout | Whenever a creature you control explores, Merfolk Cave-Diver gets +1/+0 until end of turn and can't be blocked this turn. | Fesbra

Sinuous Benthisaur | Creature | Dinosaur | When Sinuous Benthisaur enters the battlefield, look at the top X cards of your library, where X is the number of Caves you control plus the number of Cave cards in your graveyard. Put two of those cards into your hand and the rest on the bottom of your library in a random order. | John Tedrick

Spyglass Siren | Creature | Siren Pirate | Flying When Spyglass Siren enters the battlefield, create a Map token. (It's an artifact with "{1}, {T}, Sacrifice this artifact: Target creature you control explores. Activate only as a sorcery.") | David Astruga

Staunch Crewmate | Creature | Human Pirate | When Staunch Crewmate enters the battlefield, look at the top four cards of your library. You may reveal an artifact or Pirate card from among them and put it into your hand. Put the rest on the bottom of your library in a random order. | LA Draws

Uchbenbak, the Great Mistake | Legendary Creature | Skeleton Horror | Vigilance, menace Descend 8 — {4}{U}{B}: Return Uchbenbak, the Great Mistake from your graveyard to the battlefield with a finality counter on it. Activate only if there are eight or more permanent cards in your graveyard and only as a sorcery. (If a creature with a finality counter on it would die, exile it instead.) | Steven Belledin

Captain Storm, Cosmium Raider | Legendary Creature | Human Pirate | Whenever an artifact enters the battlefield under your control, put a +1/+1 counter on target Pirate you control. | Diego Gisbert

Nicanzil, Current Conductor | Legendary Creature | Merfolk Scout | Whenever a creature you control explores a land card, you may put a land card from your hand onto the battlefield tapped. Whenever a creature you control explores a nonland card, put a +1/+1 counter on Nicanzil, Current Conductor. | Fariba Khamseh