Monstrous Vortex (U 162 MH3)

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.)

uncommon
Enchantment
From the Magic: The Gathering set Modern Horizons 3.