Kiora, Sovereign of the Deep is a mythic Legendary Creature — Merfolk Noble card from March of the Machine: The Aftermath (MAT), collector number 85. Current market price: $7.26 (foil $6.46), TCGplayer market prices via Scryfall.
Vigilance, ward {3} Whenever you cast a Kraken, Leviathan, Octopus, or Serpent spell from your hand, look at the top X cards of your library, where X is that spell's mana value. You may cast a spell with mana value less than X from among them without paying its mana cost. Put the rest on the bottom of your library in a random order.