character cropping at an angle

To fit him in a rectangle or circle, dozens of ways. To crop him on that angle, not so many.  The most reliable method is to drop him into a graphics program (Paint.net is free), and almost any of them allow irregular selection and a transparent background, which is what you need. I would right click both him and the other graphic (separately), and export them as images. Then work on them as separate layers in my graphics editor. When all is done, I would save them as a single image. That way, you don't have any resizing or moving headaches.