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

Self-Reflection | Sorcery | | Create a token that's a copy of target creature you control. Flashback {3}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.) | Henry Peters

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