Most of the Final Fantasy games are broken, some more so than others. A few of them can be broken by glitches, others just through elements of the game that were overlooked before they were released. Considering I’ve only played from VI to X, those are the ones I will go through, although considering that none of bosses have immunity to status spells (like Death) in Final Fantasy II, I think that one deserves a special honorable mention XD.
Final Fantasy VI: Airship Glitch
Besides a myriad of overpowered attacks, following this method, one can gain the airship very early on in the game and, in turn, get the items and characters that comes with it, making the game very easy to beat from then on.
Although as late in the game as Ultima Weapon and Omni-slash, mixing Knights of the Round with other Materia like Mime, Quadra-Magic, or Final Attack can lead to an endless repetition of that summon which can kill any enemy.
In the disc 1 of this game you can get the Lionheart, Squall’s final weapon, using this method and after learning the L-Mag refine you can refine Tents into 100 Curagas and get 9999 health on any HP Junction.
Thievery & Dragon Crest may get stronger if you steal a lot or kill a lot of dragons, but if you get Quina down to 1 HP you can steam role the game from disc 2 onward with Quina’s Limit Glove ability which does a guaranteed 9999 damage.
Once you’ve learnt Hastega you can literally win a lot faster but Wakka’s Attack Reels is enough to kill most enemies if you train up his strength or get his final weapon. However, there is always Yojimbo’s Zanmato, which kills even the secret bosses.