Another common theme is adventure. They often go on adventures together, whether it's exploring a new part of Equestria or helping a lost animal. This allows for a lot of character development as they face different challenges during their adventures. For instance, Fluttershy might have to be brave in a spooky place, while Pinkie Pie learns to be more patient.
Friendship is a very common theme. Just like in the original MLP series, the relationship between the human and Pinkie Pie often revolves around building a strong bond. Another theme could be discovery. If a human enters Equestria, they are discovering a whole new world, and Pinkie Pie can be their guide. Or if Pinkie Pie is in the human world, she is discovering new things about humans.
One great fanfic could be 'Adventures of Fluttershy and Pinkie Pie'. It often has them going on cute little adventures in Ponyville, like exploring the Everfree Forest together. Their different personalities, Fluttershy's shyness and Pinkie Pie's exuberance, make for interesting interactions in the story.
Friendship is a very common theme. Since they are both characters from the MLP universe, fanfics often explore how their friendship develops and grows. They might start as acquaintances and become best friends, or they might have some bumps in their friendship that they need to overcome.
Adventure is also a popular theme. They might go on a quest together, like looking for a lost treasure or saving Ponyville from a mysterious threat. This allows for a lot of action and character development. In these types of fanfics, Rainbow Dash's bravery and Pinkie Pie's spontaneity often play important roles.
A frequent theme in 'mlp sad pinkie pie fanfic' is the change in her relationships. If a friendship in Ponyville sours, Pinkie Pie would be deeply affected. It could be due to a misunderstanding or someone else coming between her and a friend. These changes in relationships can bring out a lot of sadness in her character as she values her friends so much.
I'm not sure about specific 'MLP Pinkie Pie feet fanfics' as it's a rather niche and perhaps not a very common topic. However, you could start by looking on fanfiction platforms like Fimfiction. They might have some stories related to Pinkie Pie, but you'd have to search through a lot to find ones specifically focused on this aspect if they exist at all.
I haven't really come across many 'MLP Pinkie Pie feet fanfics', but if there are, perhaps they might describe Pinkie Pie's energetic movements in relation to her feet. Like how she bounces around and her feet play a part in that bounciness.
Another theme is self - discovery. Rarity is known for her love of fashion and Fluttershy for her kindness towards animals. In some fanfics, they encourage each other to explore new aspects of themselves. For instance, Fluttershy might become more assertive with Rarity's support, and Rarity might learn to be more in tune with nature like Fluttershy. This theme often ties in with their friendship as they grow together.
One common theme is loneliness. Fluttershy is often portrayed as a shy pony, so it's easy to write about her feeling alone, even among her friends. Another theme is self - doubt. She might question her abilities, like whether she's a good enough friend or caretaker.
Another theme is the discovery of self. Through their relationship, both Pinkie Pie and Cheese Sandwich might learn new things about themselves. For instance, Pinkie Pie might realize she can be more organized with Cheese Sandwich's help, and Cheese Sandwich might discover he can be more outgoing when around Pinkie Pie. This self - discovery is often intertwined with their relationship development in the fanfics.