Finely chop 10 ounces chocolate; place in a small bowl. In a small heavy saucepan, combine cream, pumpkin and spices; heat just to a boil. Pour over chocolate; let stand 5 minutes.
Stir with a whisk until smooth. Cool to room temperature. Refrigerate, covered, at least 4 hours.
Finely grate remaining chocolate; place in a small microwave-safe bowl. With hands dusted lightly with baking cocoa, shape chocolate mixture into 1-in. balls; roll in grated chocolate. (Mixture will be soft and truffles may flatten slightly upon standing.)
If desired, melt unused grated chocolate in a microwave and use to attach eyeballs. Store in an airtight container in the refrigerator.