You can find the template and tutorial here:
Victorine Originals waterfall card template.
I noticed when planning this card that the flaps do not need to be rectangles. I decided to cut out my hot air balloons so that they would appear layered in the sky (though why they are flipping up-side-down, I can't tell you). I also put the images on the back of the flaps, to add color, and cover up the ugly-Copics-soaked-through-to-the-back look.
I thought I'd take the opportunity to learn how to upload video. It was fairly trivial, at low quality. Here's how my waterfall card looks in action.
The card says "Celebrate the Journey," which was a rubber stamp included in the set of hot air balloons from A Stamp in the Hand. The other stamps in the card include a puff of wind from Rubber Monger, and trees from Hero Arts.