In a feature-length adventure, Scrooge discovers Carl Barks' ''Golden River'' deep in the mountains. but is it cursed by a mysterious gnome? In ''Law and Disorder,'' the Beagle Boys subject Scrooge to some dubious legal doings. And in ''A Midsummer's Nightmare,'' marriage counselor Fethry sends a husband-hungry spinster into Donald's life! Finally, Scrooge must save his Number One Dime from ''Coin Collector'' Melvin X. Nickelby - a threat as serious as Magica De Spell, but a whole lot nerdier.