The Lost Caverns of Ixalan

Didact Echo | Creature | Spirit Cleric | When Didact Echo enters the battlefield, draw a card. Descend 4 — Didact Echo has flying as long as there are four or more permanent cards in your graveyard. | Irina Nordsol

Hurl into History | Instant | | Counter target artifact or creature spell. Discover X, where X is that spell's mana value. (Exile cards from the top of your library until you exile a nonland card with that mana value or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.) | Eli Minaya

Master's Guide-Mural | Artifact | | When Master's Guide-Mural enters the battlefield, create a 4/4 white and blue Golem artifact creature token. Craft with artifact {4}{W}{W}{U} ({4}{W}{W}{U}, Exile this artifact, Exile another artifact you control or an artifact card from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.) | Racrufi

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