I don't find it difficult, but then I've had a lot of practice with them. I use non-stretchy fabrics like cotton and satin - the satin and other shiny fabrics give it a more polished look, but it's not always possible to find the colors you want. To do applique successfully, I strongly suggest you use a backing material to stabilize your work, such as fusible interfacing.
Thankyou SO much for the info, it is a huge help. I've been stressing over finding a professional looking way to do eyes and cutie marks without spending a fortune on an embroidery machine. I came across your eyes and thought they were beautiful, and not embroidered as per se! Thanks for the help
A layer of quilt batting between two layers of minky, to give the wings depth and shape. I make a wire frame for each wing and run a wire through the body, so that the wings can be posed, and then hand-stitch the wings to the body.