What kind of incubator do you have? You probably don't want to open it if it is a styrofoam type because all of the humidity will get out. You will risk shrink wrapping the other ducks hatching making it more difficult for them to hatch on their own. Is he moving around at all? You might have to wait until the others hatch. If he hasn't fully absorbed the yolk my concern would be for keeping him clean, but if you open the incubator and let all the humidity out you risk losing the others. That is a hard one. If he is moving around the shell will get caught on something and it will probably come off. Did he hatch on his own???