[Loved Trope] The one random episode that doesn't follow the main characters

[u/BagOfSmallerBags]

Heated Rivalry Episode 3 "Hunter": The show stops following Hollander and Rozanov's love story to follow another hockey player, Scott Hunter, and his romance with a smoothie store employee.

The Last of Us S1E3 "Long Long Time": Joel and Ellie need a car. So to explain why there's a car waiting around for them to use, they show us an incredibly heartbreaking love story lasting 20 years between two men Joel knows. They have a car.

Doctor Who S3E10 "Blink": With no explanation given, this episode begins with a character we've never met, one Sally Sparrow, poking around an abandoned building. Our lead character, The Doctor, is glimpsed seemingly randomly on TVs. What is going on? Did that statue just move!?

MythicQuest S1E5 "A Dark Quiet Death": Rather than continuing to follow our lead characters as they develop an MMORPG, we flash back many years to witness the history of a couple who start a videogame company, and how over the years the pressure to drive sales causes them to give up on their artistic integrity.

[u/lawrensaw]

Across the Sea - LOST

The only episode without a flash-side plot because the entire thing is a flashback explaining the God (Jacob) and Devil (Man in black) of the island.

[u/CustodeDiMondi → u/lawrensaw]

Speaking of Lost, there's also the episode featuring Nikki and Paulo, titled “Exposé.” If I'm not mistaken, Nikki and Paulo had never even appeared among the passengers

[u/lawrensaw → u/CustodeDiMondi]

They were with Locke and a few others but they were so unpopular they killed them off instead of giving them a chance.

[u/gahoojin → u/CustodeDiMondi]

Nikki and Paulo appear quite a lot in the beginning of Season 3, never doing anything important but just kind of being there. It’s very awkward because they just randomly appear out of thin air as if they had been there the whole time. 

The fans hated them and the writers unceremoniously killed them off in the only episode focused on them. 

[u/Baardseth815 → u/lawrensaw]

By the same token, Ab Aeterno in Season 6 would also fit this pretty well. An entire flashback episode giving Richard's origin story in the 1800's.