The most interesting part is probably the creativity of the plot. Fanfiction writers can take the basic idea of 'mlp ponies of dark water' and spin it into all kinds of tales. It could be a story about friendship tested in the face of the dark water's mystery, or a tale of a pony's journey to discover the secrets behind it. Also, the way they incorporate the elements of the ponies, like their magic and unique abilities, into the story set in this dark water context can be really engaging.
Well, one interesting aspect could be the unique character interpretations. In fanfiction, authors often explore different sides of the MLP ponies that we might not see in the original series. They can give the ponies more complex personalities or put them in extraordinary situations. Another aspect is the world - building. 'Of dark water' might imply a darker or more mysterious world, and fanfiction can really expand on that, creating new locations and rules within this darker version of the MLP universe.
Chapter 459, "Even Got Educated by a Variety Show", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Su Yinwan felt somewhat annoyed but could only suppress the emotion...
Chapter 681, "She Actually Snatched It Away?!", is the clearest early answer because it turns Miss Jiang's situation into a concrete plot event. Early on, Shao Changqing was completely in awe of Jiang Li, and after his.... By the end, President Sun is very busy today, he's still in a meeting..
Chapter 273, ""Justice Will Eventually Triumph Over Evil", is the clearest early answer because it turns Hu Zi's situation into a concrete plot event. It opens with Jiang Li, who was reading a book, suddenly jumped in fright.
Chapter 383, "Doomsday Beehive", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event. It opens with Jiang Li's pale fingertips rubbed against the handle of the coffee...
Chapter 492, "Rewarding You with Some Wild Vegetables", is the clearest early answer because the buildup finally cashes out in a real clash.
Chapter 117, "What Jiang Li Can Do, She Can Do Too!", is the clearest early answer because it turns Chixia Mountain's situation into a concrete plot event. The chapter gives readers a real answer by opening on Fragrant and cloyingly sweet potatoes and corn were out of the pot,...
Chapter 495, "It's Not Too Much to Ask for Just a Thousand Points, Right?", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Miss Su had done her homework before coming.
Chapter 378, "What if I said I have a way to find your daughter?", is the clearest early answer because it turns Kejun's situation into a concrete plot event. The chapter turns that into something concrete by moving from He Kejun's disappearance was related to an apprentice she once...
Chapter 144, "She's Too Bullying!!!", is the clearest early answer because it turns She's Too Bullying's situation into a concrete plot event. The chapter gives readers a real answer by opening on Ordinary people would have been at a loss in this situation by now.
Chapter 228, "Younger Brother is the Number One Hater?!", is the clearest early answer because it turns Madam Huo's situation into a concrete plot event. Early on, Huo Ziyang had not stepped out of the house for a whole week..