Step 1
Preheat oven to 350 degrees F (175 degrees C). Grease one 9x13-inch baking pan and two 9-inch round cake pans.
Step 2
Combine brownie mix 2/3 cup vegetable oil 2 eggs and 1/4 cup water in a large bowl. Mix with a wooden spoon until well-blended about 3 minutes. Pour into 9x13-inch baking pan and spread evenly.
Step 3
Bake brownies in the preheated oven until a toothpick inserted into the center comes out clean or with a few moist crumbs attached 28 to 31 minutes. Cool completely about 30 minutes. Cut into bite-size pieces.
Step 4
Combine cake mix 1 cup water 3 eggs and 1/3 cup oil in another large bowl. Beat with an electric mixer on medium speed until well-blended about 2 minutes. Divide batter between 9-inch round cake pans smoothing tops.
Step 5
Bake cakes in the preheated oven until a toothpick inserted into the centers comes out clean 29 to 33 minutes. Cool in the pans 10 to 15 minutes before transferring to wire racks to cool completely about 20 minutes more. Crumble cakes into large crumbs.
Step 6
Beat milk peanut butter and pudding mix together with an electric mixer on medium speed until blended about 2 minutes. Let sit until thickened about 10 minutes.
Step 7
Place 1/3 of the brownie pieces in the bottom of a large trifle or punch bowl. Top with 1/3 of the cake crumbs 1/3 of the pudding and 1/3 of the whipped topping. Continue layering remaining brownie pieces cake crumbs pudding and whipped topping ending with whipped topping.
Step 8
Cut each chocolate-covered peanut butter cup into thirds so that you have long strips. Decorate sides and top of the trifle with chocolate strips.