Well, 'mlp' stands for My Little Pony. Spike is a character from that franchise. A 'fanfic' is a fictional work written by a fan. However, the 'diaper' part makes it a bit strange. It could potentially be a very unique and niche fan - created story where Spike has some sort of adventure or situation that involves diapers. Maybe it's a comical take on the character, or perhaps it's a more serious exploration in a very different kind of story setting, but again, this is all speculation without actually reading the fanfic.
In a 'evil spike mlp fanfic', it might be that Spike has been influenced by some external dark force. This could lead to him betraying his friends and working against the values of friendship that are so central to My Little Pony. The fanfic could delve into his motives, like if he feels unappreciated or overlooked, and then show how his evil deeds play out and whether there's any chance for redemption in the end.
Well, Pinkie Pie is also a likely main character. She would be the one to throw a big 'Welcome to Pony - hood' party for Spike. She could also introduce him to all the fun and wacky things about being a pony. Rarity could be involved as well. She might take it upon herself to give Spike a makeover in his new pony form, making him look dashing and stylish among the ponies.
Yes, there are plenty of non - inappropriate Spike MLP fanfics on DeviantArt. Many focus on Spike's role in the My Little Pony world, his friendships, and his various adventures. For example, there might be fanfics about how Spike helps his pony friends solve problems or his experiences during special events in Ponyville.
The theme of loss can be quite prominent in these fanfics. Spike could lose a friendship or a special object that was important to him. This loss makes him sad and forces him to deal with his emotions. Another common theme is the struggle for acceptance. Spike tries to fit in with the ponies' world, but there are always barriers, whether it's physical differences or differences in how they do things. These themes all contribute to the overall 'sad' tone of the fanfics.
There may be some popular 'evil spike mlp fanfic' stories, but it really depends on the different fan communities. Some might be popular within a specific group of fans who are really into exploring darker themes in the MLP world. However, without extensive research in the various MLP fanfic platforms, it's difficult to name any in particular. Usually, if a story has a really engaging way of portraying Spike's transformation into an evil character and how it affects the rest of the ponies, it has a better chance of being popular.
Adventure is also quite common. Fanfics usually take Spike and the CMC on exciting adventures around Equestria. They could be exploring an ancient ruin, or trying to solve a mystery that has been plaguing Ponyville. These adventures not only test their friendship but also allow them to grow and develop as characters.
I'm not sure of a specific fanfic titled exactly that, but you could start by looking on popular MLP fanfic websites like Fimfiction.net. There might be some stories where Spike has an encounter with magical leaves or a story arc centered around leaves and his role in it.
One popular mlp baby spike fanfic might be about his adventures in Ponyville as a baby dragon. He could be exploring new places, making friends with the ponies, and getting into cute little misadventures. For example, he might accidentally set off a small magical reaction while playing with Twilight's magic books.