One of my most consistent problems with Amphibia has been its attempts to tell a serialized story using an 11-minute episode format, and I think this set of episodes is the pinnacle of why it doesn't work.
"The Root of Evil" felt like a pretty generic episode. It wasn't bad by any means, but it wasn't that spectacular, either. I did like the return of content from Season 1, but I think it could have been better executed.
"The Core and the King" needed to be a standalone 22-minute episode. It tried so hard to cram Andrias' backstory into 11 minutes that most of it felt like heavy-handed exposition. While it's nice to get more context onto some of the hint given in Season 2, we spend so little time with the new characters that it's hard to care about any of them at all. It just feels like the writers gave Andrias a brooding backstory for its own sake without taking the time to fully flesh out each character's motivations. It jumps from plot point to plot point almost as if checking off boxes of things that need to be explained without taking care to tell a good story in the process. All of this builds to a climax that feels like it was supposed to be dramatic but wasn't.