They must have, because they do that for every series.
The clip with Dento in it looks like an episode animated by Kunihiko Natsume; I'm sure of it.
i didn't consider those clips are from different episodes.
That explains the nicely animated mamepeto clip and the badly animated koromi clip.
i am guessing that first epi is by a new guy, the dento one is by natsume, mamepato's is by a good one and the koromi one is by a bad one.