Riptide Gearhulk is a mythic Artifact Creature — Construct card from Aetherdrift Promos (PDFT), collector number 219s. Current market price: — (foil $4.28), TCGplayer market prices via Scryfall.
Double strike Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.) When this creature enters, for each opponent, put up to one target nonland permanent that player controls into its owner's library third from the top.