Final Fantasy generally loves moments where heroes accidentally make things worse, unsurprisingly.
- Final Fantasy: Killing Garland in the beginning allows him to take control of the four elemental forces and create the time loop.
- Final Fantasy II: The heroes kill Emperor Mateus, who proceeds to conquer hell, and come back worse than ever.
- Final Fantasy III: The heroes defeat Xande, allowing the release of the Cloud of Darkness.
- Final Fantasy IV: Cecil gives Golbez the Earth Crystal in exchange for his girlfriend, which only helps him out in his plan for world conquest. Then they perform another MacGuffin Delivery Service. At the end of the game, defeating Zemus causes his leftover hatred to become Zeromus.
- Final Fantasy V: The heroes have already failed to stop Exdeath from breaking the crystals of their world, and then they go and kill the Crystal Guardians of the other world, letting Exdeath complete his evil plan. Near the end, killing Exdeath turns him into the near-omnipotent destructive nihilist Neo-Exdeath. (Speaking of which, who thinks up these names, anyway?)
- Final Fantasy VI: Gaining the Espers' trust and bringing them to Thamasa for a supposed reconciliation with the Gestahlian Empire just allows Kefka to massacre them all and become more powerful.
- Plus, he probably wouldn't have upset the balance of the Statues, thus setting off The End of the World as We Know It, if Celes hadn't stabbed him right before then. (Or stabbed a bit more accurately and finished him off right there, I suppose.)
- Final Fantasy VII: The heroes retrieve the Black Materia in order to keep it away from Sephiroth, but once it's been unsealed, he just mind-controls Cloud into giving it to him.
- You also kill Jenova so Holy can stop Meteor, but Holy ends up making things even worse until the Lifestream pops up to save the day. Sure, all this happens in the end cutscene without the player having any control, but still.
- And then the Lifestream ended up inflicting much of the planet with Geostigma, thanks to Jenova's cells already infecting it. Nice job making the world sick, Cloud.
- There's also the Nibelheim Incident, where Cloud proved how much of an Almighty Janitor he was by killing Sephiroth via throwing him in the Lifestream. While he effectively stopped an Omnicidal Maniac in the making, he also indirectly infused Sephiroth with Jenova and the power of the Lifestream, making him even more powerful than ever five years after his death.
- Final Fantasy VIII: Squall and the party decide to bring the comatose Rinoa to Esthar, where Odine comes forth with the idea to send her to the Esthar Lunar Base because of its advanced medical technology. Once there, Ultimecia's conscience uses Rinoa's body to release Sorceress Adel from her cryo-tomb. Nice job breaking it, Odine.
- Final Fantasy X: Surprisingly inverted, sort of. After killing the keeper of the Final Aeon, rather than using said Aeon to temporarily solve the problem, your merry group instead finds a way to end it permanently. Way to actually fix it, hero!
- Final Fantasy XIII: In Chapter 9, the party learn that Barthelandus is the Puppet Master, and he explicitly tells the party that their Focus is to kill Orphan, destroying Cocoon in the process. In Chapter 13, they kill Barthelandus, thinking that that will save Cocoon, but doing so wakes Orphan. Learning that Orphan's purpose is to bring about Cocoon's destruction, the party kills Orphan, destroying Cocoon in the process. Strange for a game whose central theme was free will. The only upside to the heroes doing it their way is that at least some of humanity survives.
- The sequel has this too: Noel refuses to kill Caius, but the latter just grabs on to his sword and kills himself. That's good, right? Wrong! It turns out that Noel just killed the Heart of Chaos, the manifestation of Etro. Thanks to that, the whole world is doomed. Oops...
- Still in Final Fantasy XIII-2, Hope leads the project to create an artificial fal'Cie and use its power for the benefit of the people of the city of Academia. Unfortunately, all he manages is to create a GLaDOS-like AI that kills him and the entire research group (which were replaced by artificial copies by the AI to cover up the incident), and leaves Academia at its mercy. Oops. Did I mention that it can turn people into undead Cie'th without marking them and giving them a Focus first? Double oops...
- The Warrior of Light in Final Fantasy XIV nearly causes a problem they were trying to fix become ten times worse. During their trip to the First in the Shadowbringers expansion, killing a light warden and absorbing their aether destroys the region's perpetual Endless Daytime and brings back the natural cycle of day and night. After they absorb a few of the light wardens' aether, the Scions notice how the Warrior of Light's soul is becoming strained from absorbing all the light aspected aether, but they let them keep doing it since no other better option is available. By the time they absorb the aether from the final light warden, the light aspected sky the Warrior of Light fought so hard to get rid of comes back since the they are now in danger of becoming a light warden themselves. Ryne does her best to help stem the effects of the aether cracking the Warrior's soul, but she notes it's delaying the inevitable at best and it's only a matter of time before the Warrior of Light becomes the very monster they were slaying left and right. Given how powerful the Warrior of Light is, them becoming a light warden would make killing them almost impossible. Whoops! Luckily, Ardbert comes in at the last moment and merges his soul with the Warrior's, buying them more time until they're able to expunge the excess light by channeling it into a weapon to kill Emet-Selch with.
- That's not even getting into what happens in the Endwalker expansion, where the Warrior of Light defeating the supposed God of Evil Zodiark, rather than saving the world, ends up causing a new, existentially more dangerous threat, to try and wipe out all life in creation.
- Final Fantasy Tactics is more or less a long string of these (as in, you're doing it for most of the game, if not all of it). In particular...
- Ramza and company saving Algus and Elmdor, both of which come back to haunt you later.
- Ramza leaving the Zodiac Stones he'd gathered with his defenseless, kidnap-prone sister. At first, this seems like a minor oops that only nets the enemy a few stones. Then, during her inevitable captivity, she is found by the bad guys and identified as the perfect vessel to stuff their dead leader into, speeding up their plan by hundreds of years. Granted, there's no way Ramza could have seen this coming, but the act itself was stupid enough to warrant a 'nice job'.
- Ramza insisting his sister stay in the monastery is another one. She tells him Ramza is a marked man, people know about him and her and will come after her. Ramza insists she stay, and surprise surprise, she gets kidnapped by people Ramza could easily beat up. Oh and despite being weak, she has a ridiculously broken buff skill that would have been hugely useful. Nice job....
- The 'Destiny Odyssey' section of the primary storyline of Dissidia Final Fantasy revolves around each hero character from the first ten Final Fantasy games overcoming their respective adversaries to acquire a crystal. Turns out that each crystal contained a portion of Cosmos' power, which weakened her enough to allow Chaos to kill her. Whoops. Granted, it was all part of Cosmos' Thanatos Gambit, but a bit of a heads-up might have been nice.
