Preheat oven to 350 degrees F. Line 18 muffin cups. Combine first four ingredients in a bowl. In another bowl, blend bananas, buttermilk, and vanilla. Beat in oil and sugar. Gradually beat in flour mixture. Stir in 2/3 cup chocolate chips.
Fill cups. Bake 15 to 20 minutes. Let cool on a wire rack.
Heat cream and corn syrup in a saucepan until mixture begins to boil. Remove from heat; add 1-1/2 cups chocolate chips. Cover; let stand 5 minutes. Stir until smooth. Glaze cupcakes with chocolate. Spoon extra into a plastic bag and refrigerate.
Cut gingersnaps to make a mouth. For ears, separate Oreo tops and bottoms and remove filling. Pipe on white frosting for eyes and top with M&M's. Snip a small corner from bag of chocolate; pipe on hair and nostrils.