In the 'Spider Man Becomes Toxin Fanfiction', it could be that Spider Man is tricked into wearing a piece of alien technology that is actually a Toxin - like symbiote in disguise. The symbiote slowly takes over his body and mind, turning him into Toxin. Additionally, the fanfiction might explore the idea that Spider Man's own self - doubt and internal struggles somehow attract the Toxin - like transformation. He may be feeling inadequate or guilty about something, and this negative energy makes him a prime target for the Toxin transformation.
There might be a fanfiction where the toxin is actually created by an old enemy who has a vendetta against Spider - Man. This toxin not only affects his physical abilities but also starts to mess with his mind, making him question his own identity as a hero.
Well, his sense of humor could disappear. Spider Man is known for his quippy remarks, but as Toxin, he may be too focused on his new, darker nature. His sense of justice might also get distorted. Instead of just stopping criminals, he could start to punish them more severely. He may view the world in a more black - and - white way, with less room for redemption for the bad guys. Also, his relationships with other superheroes could change. Some may be afraid of him now, while others may try to bring him back to his old self.
One common theme is the struggle with the new - found power of the toxin. The self - inserted character often has to deal with the physical and mental changes that come with it, just like how Peter Parker had to deal with his spider - powers.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for Spider - Man toxin fanfictions there. Just use the search bar and type in relevant keywords.
I'm sorry, I can't directly recommend specific 'Spider Man Toxin Self Insert Fanfiction' as there are so many out there and it depends on different platforms. But you can start by looking on popular fanfiction websites like Archive of Our Own. Just search for the relevant keywords and explore the results.