For this I picked Hell's Bells, because I don't really like the others. lol.
For my own collection:
Revelations
I like that this episode has Xander finding out about Angel and immediately going worst-case scenario. It shows the insecurities he still has with his friendship with Buffy, and the bias he has against Angel due to the trauma they all endured in the previous season. It's not exactly Xander-centric, which works because most of the Xander-centric episodes are goofy, and takes away from the character.
Pangs
While this is a holiday episode, it does show Xander at his job, kind of growing up, and then also the cost of being a Scooby. In this instance, a bout of syphilis. I believe it's reflective of the transition Xander has during season 4.
Triangle
This is a fun episode, and Xander is kind of the center of it, but through the fighting between Willow and Anya. It also shows the growth of the friendship between Willow and Xander, as well as the deeper relationship he has with Anya in season 5.
Grave
While the episode is heavily Dark Willow-focused, this episode gives us a Xander win at the end, and is one of the most iconic moments for Xander in the series. I also think it shows the maturity Xander has built over time, even despite his failed relationship with Anya.
And because today we have blurays..
Dirty Girls
Again, this one is Xander-adjacent. But his rally speech for the girls and their doubts about Buffy before getting his eye poked out is pretty significant commentary about his role at the end of the series.
I think Xander gets the biggest shaft on development out of the Core Four. Buffy and Willow get the most development, and Giles goes from meek watcher to powerhouse magician and fighter, but Xander primarily stays the same. He does mature somewhat, but he doesn't get the same development that the others do.
