The Sega Saturn version of Castlevania: Symphony of the Night has several differences, including more enemies, and more areas of the castle to visit.
Below are links to each of the pages showing the exclusive Sega Saturn SOTN material:
Saturn Enemies & Bosses - 18 enemies were added, 2 of them are bosses (Maria Renard and Skeleton Leader).
Saturn Maps - 4 new areas of the castle were added which contain these new enemies, Cursed Prison, Underground Garden, Soul Prison, and Hell Garden.
Saturn Monster Encyclopedia - The Saturn version has a different Monster Encyclopedia, which includes the new enemies.
Saturn Characters - Maria Renard and Richter Belmont look slightly different.
Saturn Instruction Manual - The complete Instruction Manual for the Sega Saturn version.
Saturn Case & Disc - The Saturn Case & Disc displays different artwork.