>>43653197ghost type being physical might have been because ghosts fuck shit up in the physical world. ghosts themselves are immune to physical damage, but they do interact physically when they want to (opening and shutting windows, throwing glasses, etc) IRL.
dark type being special is probably just because steel was physical and they wanted one of each. it doesn't make sense, but there's probably no good reason for it. the dark type moves were beat up, pursuit, faint attack, and bite. it's insane that they made this special. perhaps it was to give psyhic types some resistance against them, since psychics were weak to dark but also had usually pretty good special defense. who knows, honestly.