Leaf-Crowned Visionary's ability triggers when you cast an Elf spell, and it resolves before that spell resolves. You may pay {G} to draw a card even if the spell was countered or Leaf-Crowned Visionary was removed from the battlefield in response.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.