Monstrous Vortex is a uncommon Enchantment card from Modern Horizons 3 (MH3), collector number 162. Current market price: $0.34 (foil $0.37), TCGplayer market prices via Scryfall.
Whenever you cast a creature spell with power 5 or greater, discover X, where X is that spell's mana value. (Exile cards from the top of your library until you exile a nonland card with that mana value or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)