A phrase uttered with great exclamation and enthusiasm when something insanely amazing (and/or rare) occurs. Hitting a basketball with a baseball bat and landing it inside a hoop 100 yards away is a good example of a situation where this phrase merits good use. It can also be yelled or screamed in cases of extreme frustration or being angry with something, such as when being PWNED, noob fragged, or teabagged in a video or console game.
It can be thought of as a combination of "son of a bitch" + "damn" + "motherfuck."
"Son of a mother duck" is a phrase appropriate to be shouted for both epic WINS and epic FAILS. It's also more appropriate for saying by younger people who are too chicken to use adult expletives.