The big difference happens if you let him use his guard thing.

I usually just rid him of his guard and summon kotr.

game over.


One time I went through the game without summons, that made a big difference.

If you want the game to be at different difficulties use the following:

kindergarten:
use everything

easy:
don't use any bonus stat items or alternatively don't use items during battle

medium:
don't use enemy skill or summons

hard: don't use any stat boosting materia or items, and don't use summons or enemy skill

extreme: same as above, but don't use any materia more than once in battle

devastating: same as above, but no item usage during battle and no healing during battle

Insane: same as above, but you must not use any character other than cloud unless required, and then you may only use one character

Imbossibru: no materia

Demons souls (insert difficulty here): use any of the rules above, but if you die, you must start the disk over.

chuck norris: Play and beat the game without using any items, materia, limits, or the attack command, and every time you get hit you have to start the game over