Unfortunately you can't.
The Pokemon creators decided they didn't want to put that into RSE games.
I think it was because all of the glitches such as the mew trainer glitch in RB and the bad egg glitch for Celebi in GSC, that's my guess.
Hope this helped :)
No there is no way of transfering from Crystal to Emerald. Only RBY to GSC, and Emerald to all games beyond.
You can get Pokemon from the Honnen and Kanto region, and after beating the Elite Four you can get certain GSC Pokemon.
you can't get the black flute in leaf green but you can in Pokemon ruby, sapphire and emerald then trade it to leaf green.
Reach 200 owned on your national dex and Prof. Birch will give you a choice between the three GSC starters.
The population of SG-GSC is 12.
GSC Systems was created in 1984.
go to mossdeep city then head left and go past the white rock at the end their should be a house with a fisherman in it and he will give it to you
GSC Game World ended in 2011.
GSC Game World was created in 1995.
SG-GSC was created on 2000-06-18.
latios and latias appear in random patches of grass and areas of water after you catch Rayquaza or make him faint.(after saving the world in Sootopolis.)
gsc stands for gold silver and crystyl because they are all Pokemon games so gsc Pokemon are all Pokemon from Pokemon gold Pokemon silver and Pokemon crystyl and there it is you know the answer forever.