No, it is not appropriate. Tails and Cozmo are likely characters from children - friendly or family - oriented media. Writing sexual fanfiction about them goes against ethical and moral standards, and may also violate the terms of use or respect for the source material.
One popular 'tails and tails doll fanfiction' might be those that explore Tails' adventures in a new, uncharted world. Maybe he teams up with other Sonic characters in a story where they have to overcome a powerful new enemy.
You could write adventure - based fanfiction. For example, Tails and Cozmo could go on a quest to save their world from a powerful villain. This would be exciting and in line with the nature of the characters.
Characteristics can vary widely. Some fanfics may give her a more feminine sense of style while still keeping her mechanical and flying skills intact. She could be more empathetic, which leads to her being a better mediator between the often - bickering Sonic and other characters. In some, she may have a more delicate appearance but a strong will, much like the male version of Tails but with a different aesthetic.
One good 'tails vs tails doll fanfiction' story could be 'The Clash of Tails'. In this, Tails is depicted as a brave hero facing off against the rather eerie Tails Doll. It shows their different powers and how Tails uses his intelligence to try and outwit the doll. Another might be 'Tails' Duel with the Doll' which focuses more on the action-packed combat between them.
One popular 'tails x tails doll fanfiction' might be 'The Adventures of Tails and Tails Doll'. It often features unique adventures where the two characters interact in unexpected ways. Another could be 'Tails and Tails Doll: A New Bond' which focuses on them forming a special connection. There's also 'Tails Meets Tails Doll in a Mysterious World' that takes place in a strange and magical setting.
Well, given the title 'tails the fox tails is a baby fanfiction', it might be a creative work where the author has envisioned Tails the Fox in a baby - like state. Maybe it's about his early adventures or his relationships when he was very young in the context of a fan - created story. However, it could also be a very unique or abstract take on the character that doesn't follow the typical ideas we have about Tails.
There's a story about the Tails Doll where it appears in people's nightmares. It stands in a dark corner of the dream, just staring with its creepy eyes, and those who have the nightmare often wake up in a cold sweat. Some believe it has the ability to invade people's dreams because of some sort of dark magic associated with it. It's really spooky.