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 :
Buy Pokemon Crystal 2ds | UP TO 54% OFF
3DS MAx 2021 - Crystal modelling, Material, Lighting and Rendering - YouTube
Sonic Boom: Shattered Crystal - Nintendo 3DS | Nintendo 3DS | GameStop
Buy Pokemon Crystal 3ds | UP TO 56% OFF
Pokémon Crystal coming to 3DS in a cardboard box | Eurogamer.net