Ok, here's my method:
-in demo, put the Pokemon in first slot of your team
-in memory viewer, dump the RAM at D6B2 (30 bytes)
-in Kin (Japanese Gold) catch a random useless Pokemon and put it in first slot of your team
-paste via memory viewer your demo data Pokemon at D9F0
-change the ID of the first Pokemon of your team at D9E9 (HEX table here)
-if it's a generation 2 pokemon you will also have to change the first byte of the past Pokemon
ex : CB for Girafarig instead of 00?
-save if almost everything seems correct
-in Pkhex correct the nickname, the OT and sometimes the level of your Pokemon.
Edit: Got a wild Tentacruel and a wild Shark too ^^ Also Pikachu does not remain shiny
073 - ドククラゲ - 7465.pk2