Man, this was kind of a dark episode.
You have the allusion to Stoutland dying, Rotomdex calling it old, Stoutland actually looking all worn out and Litten having a nightmare where Stoutland doesn't wake up. And then you have Persian being mean just for the sake of being mean. It didn't even care about Litten's sandwich, it just wanted to cause it trouble. The fact that after the whole mess it nonchalantly came back to its trainer makes it even weirder. It's not even a wild Persian, it's a trainer's Pokemon!! How messed up is that?
I REALLY like Litten so far. Whereas Rowlet was given an easygoing personality, Litten is the complete opposite. This episode drives it home that Litten doesn't trust people easily. Litten is stubborn, mistrustful, always alert, completely violent against strangers and yet is depicted as having a warmer side when worrying about its, I guess we could call Stoutland its parent? Mentor? Whatever the case, Litten's relationship with Stoutland depicted Litten as something more than a grumpy cat who steals food, and I really appreciated it.
Another interesting thing is that Litten seems quite inexperienced at battling. It is being mentored by Stoutland, but doubtlessly it will need a trainer to realize its full potential.
I don't mind that Ash didn't get Litten. As Rotomdex said, and as Litten's behavior proved, Litten doesn't trust people easily. I am completely content with the fact that the writers are not forcing this capture and are doing it naturally, to build the friendship between Litten and Ash.
Overall, a solid episode. It seems filler-y, but it's not exactly a typical filler. Kinda like the Lana episode.