Final Fantasy 7 has several differents secret things that you may not know about, but which are very cool to do, and may even reward you with some nice items, events, or even weapons! Below is listed just some hints and tips. If you have one you'd like to send in, feel free.
Look at each of the flyer's placed all over the world and then go to Turtle's Paradise and the guy will give you 1 of each of the sources and a megalixir.
Go to the forests near Junon or Gold Saucer. Fight until you come across Mystery Ninja. Win the battle. After the battle do not use the save point on the screen. Talk to her and answer the questions in the following order: bottom, top, bottom, top, bottom. That's it.
At the Shnira Mansion unlock the safe(combo is: Right 36, Left 10, Right 59, and Right 97) and get the key to the basement. Then go into the basement and talk to Vincent before going to the library. Talk to him about Sephiroth first. Then ask about his name. He will go back to sleep again but when you go to leave after the library part he will join your party.
During the second disc go to the general store in Cosmo Canyon. The section that was roped off before is now open and you can go in the back and collect the fullcure materia, and Elixir, and a Magic Source.
In the submarine dock at the Underwater reactor pick up the Leviathan Scales. Then go to the Da-Chao mountains in Wutai and go into the fire cave. Walk into each of the fires to put them out. There will be three items: Oritsuru(weapon for Yuffie), Steal As Well Materia, and Dragoon Lance(weapon for Cid).
In the rightmost building in Kalm there is a man upstairs who is looking for 3 items. He starts his search after Meteor is summoned. Give him the Guidebook and he'll give you the Underwater Materia, which eliminates the timer on Emerald WEAPON. to find it moreph the Ghost Ship that you encounter near the Underwater Reactor. If you give him the Desert Rose, which you get from defeating Ruby WEAPON, he will give you a crappy Gold Chocobo. If you give him the Earth Harp, from defeating Emerald WEAPON he will give you each of the three master materia.
1/60 times you see the ropeway station on the Gold Saucer side you will see a guy who will trade in your Gil for GP. The rate is 100 Gil=1 GP, up to 100 GP.
Tetra Elementals are accessories that absorb fire/ince/lightning/earth damage into HP. They are very useful. Go to Cosmo Canyon and go diectly south. There will be an island there with a desert. Land and fight the cactus dudes. Morph them(they have like 4500 HP) and you get a tetra elemental. I reccomend getting 3 of them.
Get W-Item (from Midgar or Bone Village) first. Go into a battle and select the item you want to duplicate using W-Item. Use it on someone. Then pick another item and hit circle to select it but dont use it one someone. Hit X to cancel and then keep hittin O,X,O,X over and over until you get 99 of the origional item. You can do this as much as you want.
Get the Underwater Materia from the Kalm Traveler(see the secrets section for deatails)First equip all your people with Mystiles/Aegis Bracelet's as their armor and anything that increases stats as the accessory. Equip W-Summon/Master Summom/Master Magic with one of your party members. Then equip mime's on the other two. Also do Final Attack-Phoenix or Final Attack-Life 2 on all of your people. Put Yuffie in your party and equip her with the Conformer. Put 4x Cut on along with as many counter attacks as possible. Also put Enemy Skill on Yuffie. Buring the battle do a lot of W-Summon Knights Of The Round and 4x Cut. It should't be too hard. After winning you can trade the Earth Harp for each of the Master Materias.
As above equip all your people with Mystiles/Aegis Bracelet's as their armor and a Tetra Elemental/Fire Ring(but have one person have a ribbon) as the accessory. It doesn't matter what weapon because physical attack that normally do 9999, will do 100-200 damage. Just have enough materia slots. Equip two of your party members(the ones that will start off dead) with W-Summon and Master Summon/Master Magic(you should have beaten Emerald first, right?????). Equip your character that will be alive first with an enemy skill with most of the skills learned. Then equip so you have 9999 HP/999 MP. I reccomend having a mega all on each person too. Make sure your person that will be alive first also has mime. And put either Final Attack-Phoenix on one person or Final Attack-Life 2 on everyone. Start the battle by casting Angel Whisper(enemy skill) on a party memeber. Then have that party member do a Hades(to stop ruby)/Knights Of The Round summoning. The raise the other person with angel whisper. Have them cast Knights Of The Round twice. Then cast Big Guard (enemy skill) so you can have barriers and haste. The do Knights Of The Round many times and mime it. Also every once in a while cast Hades on Ruby and the tentacles behind you to stop them. He should be easy. You get a Gold Chocobo if you turn in the Desert Rose to the Kalm Traveler,and a master materia.