Preheat oven to 350°F. Line 24 muffin tins with cupcake liners and set aside.
In the bowl of your mixer, beat cake mix, pumpkin, eggs, water, sour cream, and cinnamon on low speed for 30 seconds.
Increase speed to medium and beat for 2 minutes. Fill each tin 2/3 full with batter and bake for 15-20 minutes or until tops spring back when lightly touched in the center.
Remove from oven and let cool completely on wire racks.
In the bowl of your mixer, beat butter, peanut butter, vanilla and whipping cream on medium low speed.
Add marshmallow cream and beat on medium until smooth. Slowly beat in powdered sugar until just barely mixed.
Increase speed to high and beat for one minute, until fluffy.
In a microwave safe bowl, microwave chocolate chips and oil/shortening, stopping to stir every 30 seconds until smooth. Let cool to where it is no longer hot, but still pourable.
Dip cupcakes in chocolate, frosting side down. Allow excess to drip off, then place on plate.
Top with Snickers pieces before set. Keep uneaten cupcakes stored in the refrigerator.