The best official way to play Pokémon Crystal because the save battery won't die and you can now transfer to a 3DS game for free, also restored Celebi and wireless battling :
Pokemon Crystal Official 3DS Announcement Trailer - IGN
Found my old 3Ds and found it there was some money on it and decided to buy Pokémon crystal : r/3DS
Pokemon Crystal Headed to 3DS Virtual Console | GameLuster