If the creature you control leaves the battlefield before Ambuscade resolves, Ambuscade has no effect and no damage is dealt. If the creature an opponent controls leaves the battlefield instead, the creature you control gets +1/+0 even though it won't deal any damage.
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.