Prepare and bake cake according to package directions, using a greased 13 x 9 x 2 inch baking pan.
Cool on a wire rack for 1 hour.
In a small bowl, dissolve gelatin in boiling water; stir in cold water.
With a meat fork or wooden skewer, poke holes in cake about 2 inches apart.
Slowly pour gelatin over cake. Refrigerate for 2 to 3 hours.
For Frosting: In a small mixing bowl, cream butter until fluffy. Beat in confectioners' sugar, cocoa, milk and vanilla until smooth. Spread over cake; top with candies. Cover and refrigerate until serving.