And here I return to my retrospectives.
"Swarm of the Century" is quite a stellar episode, though much like "Bridle Gossip" it relies heavily on rash decision making in the face of stress from our protagonists. There are few missteps in this episode, and characters are strongly established and move towards being closer knit.
While there aren't a lot of big laughs throughout the episode, it is consistently entertaining, and there's plenty of small chuckles to be had. The speed of events gives a consistent forward momentum, so while there isn't too much fighting there's plenty of action. This generates excitement and gives the episode some essential energy.
While watching season 4, I had forgotten how far the characters' relationships had come. I forgot that in the first season they weren't as tightly-knit as they are later on, and it's kinda surreal to realize. However, what's more surreal is the general lack of logic found when the show was primarily focused on entertaining families and had lower ambitions. How are parasprites eating words off pages? What spell could cause parasprites to eat "anything that's not food"? That's not logically possible, but in this cartoon world that's irrelevant, especially in the light-hearted, fluffy early episodes.
Some character traits are codified in this episode: Twilight doesn't respond well to pressure, Pinkie isn't very good at communication, and Fluttershy has a weakness for cute things. Some of these have appearances in earlier episodes, but here they're particularly concrete.
Ultimately, this episode is a good display of what Season 1 is. Season 1 is the story of how a group of friends became close, and it's shown here by how they learn to accept Pinkie. The nature of the first season's friendship lessons connects to the characters, and allows them to understand each other more. While this would be fine on its own, it's doubly good when establishing a further series, and builds a foundation for the future. Swarm of the Century is an episode that does that with action and energy, and it's all the better for it.