If the creature Reach for the Sky would enchant is an illegal target by the time the Aura spell resolves, the entire spell doesn't resolve. It's put into your graveyard from the stack, not the battlefield, so its triggered ability won't trigger.
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.