Final Fantasy VI: Brave New World Final Frontier

Final Frontier is a hack of Brave New World, which itself is a hack of FF6. In BNW, the goal is significant mechanical overhauls by giving everyone the same HP/MP growth (only their starting values differ) and relying on Esper Levels to improve stats, of which there are only so many levels and characters can only equip specific Espers. Other than the inclusion of Kaiser Dragon as a new boss (and a few new trapped chests), the game is basically a huge mechanical and balance modification.

Final Frontier puts that on steroids. It further limits inventory and levels, significantly improves the Stamina status (which in vanilla FF6 is useless but here it is the most important stat), modifies enemy AI to be highly aggressive and significantly different, introduces a lot additional minibosses (both in trapped chests and as random encounters), and is one of the hardest FF6 hacks out there. Its core design is "what is mechanically interesting? Include or modify it. What is not mechanically intereesting? Remove it.