Originally Posted by
Giga Guess
Try this then.
Final Fantasy X has the most Optional Bosses, some of which being the 35 extra challenge enemies in the Arena, Ultima and Omega Weapon, International Version adds the Dark Aeons and Penance, and this is just by fairly strict definitions.
Final Fantasy is one of only two FF games to give a character a phobia (Rikku's Astraphobia), the first being FFV's Bartz and his acrophobia.
Final Fantasy X is the first, and to the best of my knowledge, only Final Fantasy game to have weapons that are truly detrimental when equipped (Celestial Weapons with neither Sigil or Crest found)