FLY! to Hoenn. Enter EverGrande City and challenge the E4!
Then, in the champion room, you should see two people: Steven and Wallace. Save. Talk to Steven. Beat him. Save, but turn off in the middle of saving. Turn on, and talk to Wallace. Beat him. Save, but once more, turn off in the middle of saving. Once this is done, when you turn on once more, in that room, a third person should be standing. It is N. Talk to him. He will talk of a great distortion happening in the Unova region because some jerk is performing a mega cheat. He will ask if you know who it is. Say 'no.' If you say 'yes' and reveal yourself, N will jump out of your DS and kill you.
Anyways, go to Unova with N and watch as tiles start turning into Missingno graphics. Buildings are flickering. The 3D is completely screwed up. Screams. The people in teh game are being tortured as the game tears itself apart. You must enter the remains of the PokeCenter and access the GTS, and deposit all your Duckletts, shiny or not. You should be left with Mew and Mewtwo. Get out of the PokeCenter, and save. DO NOT step on Missingno. graphic. If your character starts flickering sprites or anything, you are screwed. Anyways, turn off.
Boot up another copy of B/W. Go to where N led you in your first copy. It should look fine, but N will still be standing there. Don't you dare talk to him. Go into the GTS, and get the Shiny Duckletss, (hope you set reasonable conditions on your first copy.) The glitch is now in your second game. Save. Turn off.
Boot up your first copy. THe glitch is gone. Talk to 'N' and he will say that the Unova region is still crying out...he will say he still feels the sorrow and that the cheater must be punished. Smash your second copy, then continue talking to 'N.' He will now say that in an alternate realm, the region has perished. And that it is up to you two to bring the cheater to justice. He will take you to Fallarbor Town in Hoenn. There you must...