1 (18.25 ounce) package white cake mix (such as Duncan Hines®)
1 1/3 cups water
1/3 cup canola oil
3 large egg whites
1 cup miniature marshmallows
3/4 cup butterscotch chips
1/2 cup chocolate-coated toffee bits
1/2 cup miniature chocolate chips
1/3 cup sweetened flaked coconut
1 1/2 cups creamy peanut butter
Preheat oven to 350 degrees F (175 degrees C).
Line 24 muffin cups with paper liners.
Beat cake mix, water, canola oil, and egg whites in a large bowl with an electric mixer at low speed until moistened. Increase speed to medium and continue beating for 2 more minutes.
Fold marshmallows, butterscotch chips, chocolate covered toffee, chocolate chips, and flaked coconut into the cake batter.
Fill prepared muffin cups 2/3 to 3/4 full with batter.
Bake in the preheated oven until cupcakes are golden brown and set, about 15 to 25 minutes.
Cool in the pans for 10 minutes before removing to cool completely on a wire rack.
Fill a pastry bag fitted with a star tip with peanut butter.
Gently insert star tip into the center of each cupcake; squeeze a small amount of peanut butter into the cupcake.