????? party overloading roaming Pokémon manipulation
By withdrawing a 16th party Pokémon at the bottom of the party via ????? party overloading, we can change the ID of the second roaming Pokémon based on the Attack stat of the 16th Pokémon.
This will allow for the creation of a roaming Celebi (251 Attack) and glitch Pokémon ????? (00, FC, FE, FF), Egg (FD) (256, 252, 253, 254, 255 Attack) in the wild, although the ????? glitch Pokémon in Gold/Silver will result in a forced link battle.
If the Egg is caught and you haven't registered its Pokédex entry (the stats of the Pokémon you withdraw may affect this), its Pokédex entry may force the game into a Glitch Dimension.
At first the roamer may be found in a glitch location until you Fly or Teleport away.
Furthermore all roamers use the Legendary Beast music in Crystal even if their species is wrong.
If possible, it's wise to catch or hatch an Egg of the roamer you want to find so you can view its area in the Pokédex.
- ChickasaurusGL (article text with permission, video, documentation)