Pokémon Crystal has been confirmed for release on the Virtual Console on January 26th 2018. This will have connectivity with the Generation 7 games and also encounter Celebi within the game. In the Japanese version, when you beat the Elite Four and go to the Pokémon Communication Center in Goldenrod City, you'll be gifted with the GS Ball. It's currently unclear what the method will be in America and Europe
A physical version will come in Europe on January 26th 2018 which contains the download code in a box, while in Japan a Physical edition is coming with a magnet based on its cartridge, stickers and a poster of all the Pokémon
We covered this game in full back in 2000 so be sure to check our section for full details