Chocolate cupcakes filled with 'slime green' cream cheesiness and topped with buttercream skulls. Peanut M&Ms and chocolate Jimmies provide the decorative details.
Lessons: Use plain M&Ms for eyes since they're more uniform (some of those peanuts are huge) - or combine plain and peanut for a kooky look without worrying that the eyes will overwhelm the skull outline. Also, mini-chocolate chips would make a better nose (hole). Jimmies make cute "teeth," but buy a large container of Jimmies (the one I had is part of a four-compartment combo pack so it was slim pickings for similar sizes) and invest in a pair of kitchen tweezers.