I think there should be a video (gif) like the one in the window when you view monster info.

I think (and I've definitely checked) that there isn't such a video in the default resources of Heroes, because, for example, let's take the unicorn animation.
This animation is used for displaying it both on the battlefields, which have different backgrounds, and in the castle...
It doesn't make sense to store all unicorn animations combined with different types of backgrounds.
It's much more efficient to store only the outlines of the moving image (the unicorn).
By the way, the turquoise color on which the moving images are located is not a background, but rather its absence (transparency).

The question about the executioner is interesting to everyone, I think!!!

I'll need to dig around a bit more.