The two key frames (first and last) were fully drawn by our artist. Previously we just crossfaded between the two frames in-game, hoping to achieve an animation effect. Now we've added in-between frames created by an interpolation script — similar to frame generation in modern GPUs, not like AI generation by prompt. So the result you see, from the overall composition down to the small details, was determined by a human, not a random number on a server.
Here's the tool we used: https://github.com/hzwer/ECCV2022-RIFE. The only interpolation artifact I'm aware of is the pattern on the MC's outfit — since it's a fairly basic technology, it just blends the two frames and the pattern gets lost. Other things that might seem odd to you could be due to the two drawings being drawn differently from each other.