Goblins and ghosts are not the only elusive phantoms this season. ""Like whispered rumors of strange happenings,"" the eight tales in The Hidden Folk: Stories of Fairies, Gnomes, Selkies, and Other Secret Beings by Lise Lunge-Larsen, illus. by Beth Krommes, were ""originally told as fact,"" according to the author's source note. The tales of mysterious Northern European creatures inspire enchanting scratchboard illustrations in a folk-art tradition, featuring ruddy, rotund humans while brightly clad fairies lurk among leaf fronds and selkies take refuge in the sea. ( Aug.) .