If the damage that would be dealt by Rile is prevented, the creature still gains trample until end of turn.
29-09-2017
wotc
If Rile targets a creature with 1 toughness, that creature won't be destroyed until after you've drawn a card. Its abilities may affect that draw or trigger on that draw if appropriate.
29-09-2017
wotc
If the target creature is an illegal target by the time Rile resolves, the entire spell doesn't resolve. You won't draw a card.
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.