International trades involving Japanese games can be performed in Pokémon Red, Green, and Pokémon Blue (Japanese) or Pokémon Gold, Silver and Crystal with specific requirements. Due to these trades being unsupported, the Pokémon usually become a different Pokémon.
Special methods can be used to obtain Pokémon of the player's choice.
Red/Green JP with Red/Blue EN
Receive any Pokémon:
This technique, known as the remaining HP glitch trade method, can be used to obtain any Pokémon/almost any glitch Pokémon in English Pokémon Red and Blue. The player must have a party of six Pokémon on both sides.
When trading between Red/Green and Red/Blue, the data is loaded incorrectly. By chance (it will always work though), the Pokémon Red/Blue receives from Red/Green Pokémon 5 depends on Red/Green Pokémon 1's second HP byte (ranging from 1-256). This means then, without further complications the player can obtain all 151 Pokémon and all glitch Pokémon using specific remaining HP matching that Pokémon's index number (not Pokédex number).
The Pokémon is a hybrid, but (for regular Pokémon) will be added to the Pokédex.
If Pokémon 1 has 21 remaining HP, it will give out Mew.
Due to its likely unterminated name, the player may need to view a Pokémon with no move 4 before depositing/releasing it. The player may also need to deposit the Pokémon directly above it (if party terminators get glitched). These steps will prevent a freeze when selecting the glitched Pokémon/opening the party.
Gold/Silver/Crystal JP with Gold/Silver EN
This glitch allows the player to receive ????? on English Gold/Silver.
To perform this glitch the player must have six party Pokémon in the Japanese version, but only one party Pokémon in the English version (it may also be required (but not confirmed) to be at the point in game where the player has only just got access to the trade center on the English version. This is a precaution that ensures the Pokémon will be ?????).
Attempt to trade Pokémon 1 on the English version and attempt to trade Pokémon 6 on the Japanese version. This will allow the player to trade for ?????. On the English version the game may freeze with a white screen, but if the player waits until the trade is complete on the Japanese version and resets the game, the English version will have the ?????.
- ChickasaurusGL (documentation, video, text)