[Philbro]

To access the Secret Duel, you have to trade in enough BP for the
W-Summon materia and Omnislash, and you need Cloud's ultimate weapon,
the Ultima Weapon, which you get from Ultimate Weapon (^_^). Cloud is
the only party member that can participate in the Secret Duel.

well to Access the special battle u want u should have the follow:

Enough BP to get the W-Summon Materia and Omnislash
U also need to get Cloud's Ultimate Weapon which u get from Ultimate Weapon. Guess what the name is also Ultimate Weapon.

Remember Cloud is the only one who can do this duel :P

Hope that helps. Ok NEXT QUESTION:

I havent had much experince there im afraid but the above advice can really help Using the save crystal is the way i would do it also.