Prepare brownie mix according to package instructions and bake in a 13"x9" pan. Let cool.
For the frosting
For the buttercream frosting: Beat butter with an electric mixer until creamy. With mixer on low, gradually add powdered sugar and milk (or water). Once it's combined, turn mixer to medium and beat for 3 minutes. Set aside.
For the cute critter assembly/decorations
Use the round cutter from the Wilton DIY-lish Cute Critters Decorating Kit to cut brownie circles. You should have 12 total. Save leftover brownie pieces for later.
Frost each brownie with buttercream frosting.
Follow instructions to decorate the brownies with the Wilton DIY-lish Cute Critters Decorating Kit.
Note: Frost extra brownie pieces to enjoy as a snack.