This was pretty damn impressive, best animation was clearly saved for this episode, it genuinely felt tense and atmospheric. Only complaint is them once again using stock XY music at the start. A shame they only used a small excerpt of the actual Title Defence theme for this entire 4 episode battle. The other music choices worked fine though.
Loved how bro-like the Pokemon/trainer combinations were here, with Tapu Koko even high giving Kukui. His league has clearly been given the deity seal of approval.
I feel like I would have been more invested in Nagnadel vs Tapu Koko if Ash had remotely trained, but ultimately they were two 'guest' Pokemon anyway so it doesn't really break things too bad. The main highlight was of course Pikachu vs Tapu Koko. I admit it's kind of weird that Pikachu is doing so well here, given he couldn't even scratch Tapu Koko in earlier matches. It's less about progression series wide, he certainly has done a lot in Alola, but more show wide, Pikachu was already pretty buff from the start of SM. Though in fairness he did use Electroweb and 1000 volt Z Move for the first time against it.
The character reactions made this, especially Ash and the other companions' reactions to him winning.