Complex pop-ups really are inspired by what kind of movement you're looking for. If you want someone's arm to come out, how are you gonna make that happen? If you want a spaceship to go across the page it's usually a matter of movement or anatomy. Instead of just having a whole body pop-up, how do I articulate that body? A lot of complexity comes out of that.
Really inspiration comes from the movement and how slowly or how fast you want things to open. Everything's built off of basic principles in pop-ups. The v-fold, the layer, pull tabs and then rotators and variations of that. Sometimes a little bit of magic as well.
In our studio we've created one of our tallest pop-ups before and that's in the Jungle Book. It's a monkey tower and it opens and it opens and it opens totally like this giant tower with monkey's crawling all over it. It's basically layers and v-folds, but it's how you connect them and how you put them together. That's how these complex pop-ups come together.