HEAT oven to 350°F.
PREPARE cake batter as directed on package. Add dry pudding mix, cocoa powder, violet food color and 2 tsp. blue food color; mix well. Spoon into 24 paper-lined muffin pan cups.
BAKE 18 to 21 min. or until toothpick inserted in centers comes out clean. Cool cupcakes in pans 10 min.; remove from pans to wire racks. Cool completely.
ADD remaining food coloring to frosting; mix well. Spread onto cupcakes. Decorate with remaining ingredients to resemble monsters as shown in photo.