From the first games for GB know of the existence of this "pokemon" produced from a programming error of the game or intentionally (as in the GBA versions)
Now the main question ..
Is it valid or not this "Pokemon" (It may be legal because the game NOT generated naturally) ..
The funny thing is that there EXIST in all games (All pkmn versions,PBR, MPR & PKWalker) and is perfectly playable and stable ..
I open the question as I am intrigued by the fact that there pkmn in the game and has his own pokedex number (494 and 495) besides "name" Egg & BadEgg
If you want I can post it (it passes tests of legit) to see what it thought..
Here for download
http://www.megaupload.com/?d=EL3OJZPH
They can play with these in PBR can put them MPR and Pokewalker ..
Whatever happens NOT exchange them via GTS as this will not be permitted and no longer remove them or let them share there...
Excuse my English.