As title, even though it's a single ability and the item says abilities deal bonus damage, it's only the first target that the single ability hits that deals bonus damage. Now obviously for something like a DoT only having the first instance of damage getting the bonus damage makes sense, but for something like Grey Talons arrow it's a bit counter intuitive that it only works on a single target that was hit unlike other abilities like Bebops bombs which applies to everything that is hit by it's explosion.