I know a guy who was exploiting the diamond/pearl multiplication glitch to get a second dialga, and his requested pokemon in return was a level 100 female magikarp. Luckily for him, the glitch worked, so he got a dialga, but his original non-cloned one had been traded.
As far as we can tell, somebody used a gameshark or something to make a ton of level 100 sucky pokemon in a different pokemon game, imported them, and used them to trade for dialgas and the like.
Now that I've completely derailed the topic, I taught my Dialga a bunch of HMs because I was headed to the elite four and all my other pokemon were better. I didn't really feel like turning back so I just screwed over my legendary.
