Perhaps in the fanfiction's alternate ending, Padmé doesn't die. Anakin realizes his mistake in time, and together they manage to expose Palpatine's true nature to the Galactic Senate. This leads to a new era of peace and cooperation, with Anakin using his skills to train a new generation of Jedi, and Padmé leading political reforms to prevent such a power - hungry dictator from rising again.
One possible alternate ending could be that Anakin Skywalker resists the dark side at the last moment. Instead of becoming Darth Vader, he uses his love for Padmé to find the strength within him to reject Palpatine's temptations. This would change the entire future of the Star Wars galaxy, as there would be no Vader to enforce the Emperor's will, and the Jedi Order might be able to be rebuilt more quickly.
One possible alternate ending could be that Twilight Sparkle uses her magic in a completely unexpected way to stop the wedding chaos and actually uncovers a plot that was much deeper than anyone thought, leading to a celebration of friendship rather than a wedding.
In one alternate ending, Ariel might not choose to be with Prince Eric. Instead, she realizes that her true place is in the sea with her family and friends. So she gives up on the idea of becoming human permanently and returns to her mermaid form, ruling the underwater kingdom beside her father.
One possible alternate ending could be that the heroes discover a way to reverse the damage caused by Timetagger without having to fight him directly. Maybe they find an ancient artifact that has the power to reset the time changes he made. This would lead to a peaceful resolution and the restoration of the original timeline.
In a different take for an alternate ending, the Phantom could expose his face to the public in a grand gesture. He shows that despite his disfigurement, he is a man of great talent and feeling. The public, moved by his music and his courage, accepts him. Christine then falls in love with the new - confident and accepted - Phantom, and they build a life together where the Phantom becomes a respected figure in the Parisian art scene.
One possible alternate ending could be that Iron Man and Captain America come to a truce much earlier. They realize that the real enemy is the outside force that has been manipulating them all along. So, instead of fighting each other, they join forces and expose the true villain, leading to a united Avengers once again.
Fanfiction can change the tragic ending by simply changing one key decision. For example, if Anakin decides not to trust Palpatine's lies about saving Padmé from death. This one change could lead to a completely different outcome where Anakin remains a Jedi and the Sith's plot is foiled.
One possible alternate ending could be that Jafar actually manages to outwit Aladdin in the final battle. Instead of Aladdin winning and getting the girl and the kingdom, Jafar takes over completely. He turns the kingdom into a dark and desolate place, with all the citizens living in fear. Aladdin is banished to the desert, and Jasmine is forced to be Jafar's prisoner. This would be a much darker and unexpected ending compared to the original.
Another view could be that the alternate ending is a way for fans to explore different narrative paths. It could be a way to satisfy those who felt that the original ending was too sad or left some loose ends. It might introduce new plot elements, like new characters who play a significant role in changing the outcome for Hazel and Gus. It could also be a means to explore different themes, such as the power of love in a more positive light, rather than the bittersweet way it was presented in the original.
Another alternate ending could be that there is a big battle between the living and the dead. Victor manages to broker a peace treaty between the two worlds. As part of this, the Corpse Bride is given a special place in the living world. She becomes a sort of guardian between the two realms, and Victor stays with her as her companion, and they both ensure that the living and the dead co - exist peacefully.
In an alternate ending in fanfic, the spell could have been broken in a different way. What if instead of Belle's declaration of love, it was the Beast's selfless act towards the villagers that broke the spell? For example, when the villagers come to attack the castle in fear, the Beast could have chosen not to fight back and instead protect them from some other danger. This act of kindness and selflessness could have been the key to breaking the spell, and he turns back into a prince. Belle then realizes she has fallen in love with him not just for his new form but for his noble heart.