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Need more links..

FF6 Hacking
Host of this wiki!

Slick Forums
Lots of knowledgeable FF4 and FF6 folks hang out there!

Mnrogar's Den
Registrations are closed but it's a good source of info about FF3us.

My Barren Webpage
Webpage of assassin, veteran hacker, that host many patches that are mostly bugfixes. You can also find on this site a commented C2 disassembly and other documents.

Imzogelmo's Not-Even-Penultimate ROM Resource Here you can find patches and essential documents for event editing such as the event dump and event commands list.

Slick Productions Good resource for disassembly docs (bank C0, C1 and C3 most importantly). They host a variety of patches, including their Pandora's Box hack.

ZED's Unoriginal White Sheet Host of various hacking documents and original patches. There is also FF3us documents such as the Sketch bug guide.

Leet Sketcher's Patches for Final Fantasy III/VI Website hosting various recent bugfixes patches.

SilentEnigma's Cool Things Site of a hacker that came out of the grave. Host a few patches.

RPG Legion Patches, utilities and documents like the enemy command script guide and commented C2 disassembly.

Drakkhen's Patch Pages Host of some patches, utilities and a partial FFVI Advance ROM map.

Geiger's Crypt Some patches, utilities and the incredible snes9x debugger.