So I've completed FFX once, just about with a lower "level" party than I realised. But I was wondering how to extend the longevity of the game, apart from the whole 100% completion thing. I found a nice list actually.
NSG - No Sphere Grid. Don't activate a single node on the Sphere Grid.
NS - No Summon. Don't summon an aeon. Except for the four forced Summons.
NC - No Customise. Don't use the "Customise" ability in the menu. You are
allowed to upgrade a Celestial Weapon to their full power, though.
NO - No Overdrives. Don't use overdrives, except for the two forced ones.
NE - No Escape. Don't escape from a single battle.
NNE - No [No Encounters]. Don't use the weapon/armour ability [No Encounters]
NBB - No Blitzball. Don't play Blitzball for rare items.
But I'm going for a Single Character Challenge. Maybe Tidus first I reckon. But I have this fascination with the water-loving characters Tidus, Wakka and Rikku. I might just power them up and see how it goes. Anima will probably be very difficult but it'll be interesting. So probably a TWR challenge for me.