I don't know what glitch this is, but I remember years ago back when I still had my Crystal version, I used duplication glitch to get another Lugia and I ended up with a Pokemon named ??????????????? with a Lugia sprite. All of its stats had question marks o.o Every time I sent it out in battle, my game would crash. And when I put it back into my PC, random level 0 Pokemon would pop up in its box. It was so weird.
Edit: Derp just bothered to read the posts on this page fully. So it was a bad duplication, huh. I had figured it was something different lol.