Some characters might be amused. For example, Sans would probably make some witty remarks about the fanfiction's plot twists. Papyrus, on the other hand, might be a bit confused at first but then get really excited if he finds a heroic role for himself in the fanfiction.
Well, it could be that the battles are more about strategy and friendship. Since both Undertale and Pokemon have elements of non - violent ways to progress. In the fanfiction, a trainer might use their Pokemon's friendship levels and abilities in a way similar to how Undertale characters use their relationships and skills. Maybe a Pokemon's loyalty can be used to break through an enemy's defenses, like how in Undertale, kindness can sometimes end a fight.
Some people would be shocked and immediately look away. They might be too embarrassed or uncomfortable to even stay in the area. Others might try to help the person by covering them up or calling the authorities. There would also be those who would laugh or take pictures, which is quite unethical but unfortunately happens in real - like situations in stories.
I often find that the best death battle fanfiction are the ones that not only focus on the fight itself but also explore the characters' emotions and motivations. It adds depth to the story. Like, a character's reason for entering the death battle could be more than just for power or glory, it could be for revenge or to protect someone they love.
Most probably not. Usually, such titles suggest a fictional or imaginative storyline rather than being based on actual happenings. It could be a work of pure imagination or inspired by various fictional elements.
Well, if Undertale could watch Undertale fanfiction, it could lead to some chaos. For example, Sans might make jokes about the wild scenarios in the fanfics. Papyrus, on the other hand, might be eager to correct any misinformation about himself. And Flowey could use it as a way to manipulate things further, seeing how the fans view the characters and using that knowledge to his advantage in this strange, meta - situation.