Snorlax in R/B/Y was unique (well, there were two, but i mean you can't find in grass), in G/S/C there was sudowoodo. You need a item to obtain it (like spiritomb, you need the odd keystone.). spiritomb doesn't have incredible base stats, it's only at level 25, it's not in a hidden place. it's only u, and quite difficult to obtain, but not legendary. :3