This is an exercise I've always loved doing, and is actually how I mostly learned how to draw growing up; taking a still from a movie, video game, or even images in books, and redrawing them just by observing them. I remember the first dragons I drew were from old DnD books I still have! I grew pretty good at observation drawing based on that, but I haven't done it in so long that I kind of lost touch with it. It's nice to go back to these sorts of basics!
These shots are from the Blue Exorcist movie, during one of my favourite scenes.