Great, I think that the Jenova-fight will be the kickass!
Here are some more ideas:
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The sick man in Midgar:
There is that sick man in Midgar in the tube on sector 8 near the church on CD-1. Can you make that when on CD-3 you can get back to Midgar with the key, the man is there, and ask you to deliver something (the potion) for him? Then He gives you mysterious talisman that you need to use fore something (Example deliver it for somebody else)
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Save Crystals:
Add two more Save Crystals in the Northern Cave (My personal opinion of course)
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Rare enemy fight:
Make some nasty enemy on CD-3 that is very very rare and you can encounter it anywhere. But like so that you can beat it only once, and get the great reward.
Example: Mysterious Pot
HP: 100 000 or lower (It need to be tested how hard it is when he/she mimics everything)
MP: Full
Attacks: Mime (Copy your last move)
Special: Wants some item
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Sephiroth's Clone fight:
Use Sephiroth's model to make this fight. Fight is optional and is located on Nibelheim reactor on CD-3
Stats:
HP: 200 000
MP: Full
Attacks: Ultima, Shadow Flare, Physical Attack, Cure3, Wall, DeSpell
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1 / 35 Soldiers:
Make them actually 35 and HIDE! them all over the world, make it non-sell and non-use item. But DON'T! hide them in places where you can't get than once
When you get every soldier, you need to use them for something and you get the great reward.
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Ancient City and The White Materia:
After Aeris dead, you can't get to that place 'cause of that bastard MR. FISH AND THE GANG (the algae). Make it so that you can bribe them for entering that place. You need to pay 1 000 000 every time you enter.
But you can get the White Materia from there.
Okey, that bribe thing was kinda a joke, but it would be super cool if you can do that
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That was all today, tell me how you like them