Fused for iOS is a simple and straightforward app that helps you superimpose two images or videos over each other. It works well, but is kinda a "one trick pony".
Fused presents in portrait mode to deliver a simple and modern interface that's completely user friendly and easy for anyone to follow, regardless of skill level. Basically, all this app does is superimpose 2 images, videos, or a combination of the two; one atop the other. In other words, this is a one hit wonder of an app, because that's virtually all it does. To make the magic happen, just select a source for your foreground, and another for your background. After that, you just set the opacity, perhaps apply a basic filter or two, then render the finished clip or pic to save and share in the usual ways.
The interface has some novel elements to it. I liked how your source images appear as smaller thumbnails below, with your combined new clip showing live renders of your filtering up top in a large thumbnail. In between these; center screen, is where your tools appear. The tools themselves are rather sparse, with the best offerings available ala carte for purchase.
Fused is good at what it does; it just doesn't do much. Personally, I'd suggest getting a good video editing app instead because it will do the exact same thing, plus open you up to a world of greater possibilities.