The Lost Caverns of Ixalan

Frilled Cave-Wurm | Creature | Salamander Wurm | Descend 4 — Frilled Cave-Wurm gets +2/+0 as long as there are four or more permanent cards in your graveyard. | Aaron Miller

Ojer Pakpatiq, Deepest Epoch | Legendary Creature | God | Flying Whenever you cast an instant spell from your hand, it gains rebound. (Exile it as it resolves. At the beginning of your next upkeep, you may cast it from exile without paying its mana cost.) When Ojer Pakpatiq dies, return it to the battlefield tapped and transformed under its owner's control with three time counters on it. | Chris Rahn

Waylaying Pirates | Creature | Human Pirate | When Waylaying Pirates enters the battlefield, if you control an artifact, tap target artifact or creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.) | Zoltan Boros

Deepfathom Echo | Creature | Merfolk Spirit | At the beginning of combat on your turn, Deepfathom Echo explores. Then you may have it become a copy of another creature you control until end of turn. (To have this creature explore, reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.) | Matt Stewart