First, a link to the free Beneton Movie GIF Maker... the best animator I've seen.
Then a collection of animated book covers. Note that while some of these involve sophisticated animation art, some are very simple and could be done easily with what you already know about paint.net or other graphics program.
Just think in terms of using a second layer to add things like the blood on the throat, or falling leaves or ripple effect... then saving separate images to create a sequence to animate. Many use effects that are built in, such as the ripple, the rotation of the saw blade, etc.
Even the lightning stroke might look difficult, but is actually just a matter of placing a stock lightning image on the design, then erasing it bit by bit from the bottom, then running the "frames" in reverse order to create the effect of it striking downward.
