Etali, Primal Storm is a rare Legendary Creature — Elder Dinosaur card from The Lost Caverns of Ixalan Commander (LCC), collector number 224. Current market price: $0.55, TCGplayer market prices via Scryfall.
Whenever Etali attacks, exile the top card of each player's library, then you may cast any number of spells from among those cards without paying their mana costs.