For the cupcakes: Preheat oven to 350F; line a cupcake tin with paper liners.
Sift flour, cocoa powder, baking powder, baking soda, cinnamon and nutmeg in a bowl; set aside.
Combine buttermilk, pumpkin and vanilla in a bowl; set aside.
Beat butter and sugars together in a large bowl with an electric mixer on medium speed until fluffy. Add eggs, one at a time, beating well after each addition, until the mixture is smooth and light. Alternately add flour mixture and buttermilk mixture, blending well after each addition.
Divide batter evenly among cupcake liners. Bake for 18-22 minutes, or until a toothpick inserted in the middle comes out clean.
Cool cupcakes completely, then using the cone method, fill cupcakes with pumpkin buttercream (recipe follows).
Frost each cupcake with chocolate frosting (recipe follows), then dip the frosted tops into the finely crushed Oreos to evenly coat. Stick an Oreo Fudgee “tombstone” into the top of each cupcake, and place a zombie hand in front of it.
For the pumpkin buttercream: With electric mixer, cream butter and pumpkin (mixture will look grainy). Turn mixer to low and add cinnamon, ginger, salt and vanilla. Slowly add 1/2 cup confectioners’ sugar at a time until the buttercream is creamy and no longer separating (the mixture will look grainy if there isn’t enough sugar mixed in).
For the chocolate buttercream: Beat butter and cocoa until smooth, then add sugar 1 cup at a time, beating until smooth with each addition . Add milk and vanilla and beat for about 3 minutes.