I found there are 3 secret keyblades that are unlockable that are not listed anywhere. I have been able to recive the Anti-Key and the Lost Heart. I am working on the Final Key. But for some reason these did not work for 2 friends of mine as they did everything for them but when they walked up to the mural they did not recive them. So it may not work for your game either.
Anti-Key ATK: 10 STR: +8 MP: -1
The first hidden key is seen in Neverland. If you remember the fight with that Anti-Sora, you'll remember he was fighting with a black version of the Kingdom Key. This keyblade is called the Anti-Key. To get it, you must do the following:
1. Unlock all the chests in Neverland
2. Aquire all 12 of the hidden items from Big Ben's doors
3. Defeat the Phantom at Big Ben
After you complete all that return to the Secret Waterway in Traverse Town and walk up to the mural of the moon.
Lost Heart ATK: 11 STR: 9 MP: +1
The second key is seen in Hollow Bastion. During your 2nd battle with Riku, you'll see he's using a new key. To aquire this keyblade you must do the following:
1. Unlock ever trinity in the game (46 total)
2. Seal Hollow Bastion
The return to the Secret Waterway and walk up to the mural of the moon.
Final Key ATK:13 STR: +10 MP: +3
This is the key you dream about at night. This is why you have played the game. This is a keyblade masters dream. Anyways... After you beat that psyhco Ansem for the final time and he sees the light, you see Mickey beyond Kingdom Hearts with what appears to be as another kingdom key. Well, if you look at it you will see that the silver and gold colors are switched around! So the golds on the blade and the silvers on the handle. So you might think, why the hell is it like that? Because, it is the final key and the only way to snag that baby is to complete 100%, yes 100% of the game. That means all...
1. weapons (Sora, Donald, Goofy)
2. chests
3. bosses (normal and hidden)
4. tasks in 100 Acre Wood
5. all competitions with your team, alone, and time trials
6. body parts for the gummi ship
7. trinitys (which will get you the Lost Heart)
8. lock all worlds
ALL THAT you might say? Well, get crakin' cause it may take longer than it looks. Then once you have done everthing go to the mural of the moon and obtain this increadible weapon. Of course I don't know what your going to do with it since it is so destructive and if you could battle Sephiroth again it would probably kill him in 10-13 hits. But whatever your going to do with it, have fun!
Remember these may not work for you as I said earlier that 2 friends of mine had a problem with them.
GOOD LUCK!!!!
