Oracle Text

Target creature you control gets +1/+0 until end of turn. It deals damage equal to its power to target creature an opponent controls.

Card Rulings

7/14/2017 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.