Here's what I have to say regarding the story structure of Amphibia.
Season 1:
The first season consists of 20 episodes, which can all be split into 4 sections regarding its story structure.
- Episodes 1-5 help to not only set up the main character's personalities, but also Anne's relationship and dynamic with the Plantars. Anne not only becomes best friends with Sprig, but also develop a big sister and little brother type relationship. Polly is skeptical of Anne at first, but they develop a sister like relationship. Hop Pop is the parental guardian/authoritative figure that butts heads with Anne's rebellious/care free attitude, but grow to like and respect each other as people.
- Episodes 6-10 help to develop Anne's relationship with the town itself. Now that she has to venture more into the town of Wartwood, she has to deal with how others perceive her. At first, the town doesn't trust or like her, resulting in everyone treating her with disrespect. It's only when she stands up for the town that she's finally given respect and is accepted as a citizen.
- Episodes 11-15 help to develop Anne's relationship with more of the individual characters that inhabit Wartwood like Wally, Maddie, and Mrs. Croaker.
- Episodes 16-20 help to show not only just how much of a difference Anne has made ever since she was transported to Amphibia, but also how much she herself has changed. Her time with the Plantars, the Town of Wartood, and all the crazy adventures she's been on has helped her to grow as a person and be better than she was when she arrived. All this culminating in the season finale where Anne faces off against Sasha, after realizing how much of a toxic friendship they’ve had for most of their lives.
Season 2:
The second season also follows a similar structure to the first season with its 20 episodes.
- Episodes 1-5 show Anne and the Plantars’ new journey to travel to Newtopia. We finally get to go outside of Wartwood and explore more of the world of Amphibia, resulting in new kinds of adventures for the main characters.
- Episodes 6-10 show life inside of Newtopia and the wonders to explore in such a kingdom. It’s also through these episodes that were given more answers as to what the music box is and how it works.
- Episodes 11-15 show our main characters returning to Wartwood and giving more focus to some of the other side characters that haven’t gotten enough screen time. It’s also through these episodes that we visit the three temples that restore the power of the stones and what they each represent.
- Episodes 16-20 help to develop the growing conflict between the group of characters. Sasha’s inner conflict about manipulating her friends, Marcy’s secret deal when returning the music box, and Andrius’ true intentions about using the music box. All this culminating in the season finale, where everyone’s “true colors” are shown and the fight for the music box takes place.
Season 3:
The third season is the only one with a different structure compared to the previous two seasons.
Seeing as how this is the third and final season with only 18 episodes, it does have a bit of a different structure compared to the previous two seasons.
- Episodes 1-10 sees Anne return home and the Plantars travel to Earth for the first time. These episodes are important for different reasons. Firstly, since most of the show has spent time in Amphibia and showing why it’s worth saving, it’s equally important to spend time on Earth and show why it’s worth saving as well. Anne’s parents, many of the people they’ve met and made friends with are reasons why they need to stop Andrius and the Core’s invasion. Secondly, it helps to show the urgency of the characters’ current situation because while they can enjoy things that Earth has to offer, they also need to find another way back to Amphibia and stop Andrius.
- Episodes 11-18 sees Anne and the Plantars return to Amphibia, but in a state of oppression and many of their friends/allies forming a resistance against the upcoming invasion. These episodes are important because they show everyone throughout the entirety of the show coming together to stop the big threat. All this culminating in the series finale, where everyone’s story arc comes to an epic and bittersweet conclusion.