Riddleform is a uncommon Enchantment card from Hour of Devastation (HOU), collector number 43. Current market price: $0.06 (foil $0.13), TCGplayer market prices via Scryfall.
Whenever you cast a noncreature spell, you may have this enchantment become a 3/3 Sphinx creature with flying in addition to its other types until end of turn. {2}{U}: Scry 1. (Look at the top card of your library. You may put that card on the bottom.)