Overlord Season 4 Episode 13 knew what it wanted to be and perfectly executed its plans. It is just that those plans were bad to begin with and couldn't be saved by anything the show did.
Overlord Season 4 Episode 12 was a decent episode that featured a lot of great moments and tied up a few knots that didn't need to be tied. The build to the finale has been weak.
Overlord Season 4 Episode 10 was a huge improvement for a show that desperately needed it. Things aren't back to normal just yet, but we are getting there, and at this pace, the ending might just be a great one.
Overlord Season 4 Episode 9 was fundamentally sound but uninteresting, which has been the story of this entire season so far. There just aren't enough new things happening in the show to retain the audience's interest after 8 years of it being on air.
Overlord Season 4 Episode 8 was an outing that was frankly boring to consume. The show doesn't have much going on right now, and it better straighten that out, lest it risks losing the attention it has retained up to this point.