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The Japan-only Goldenrod PokéCom Center has a unique BGM which is apparently enabled "after unlocking the Pokémon Mobile System GB". However, I can't find either the BGM or the Mobile System GB switch in English pokecrystal. Does it exist? If not, can I get some help adding it in?
ROM hack: Pokémon Polished Crystal — version 2.2.0 released!