Preheat your oven to 350°F (177°C) and grease a 9"x13" baking pan with non-stick spray. Line with parchment paper for easy removal.

Prepare the brownie mix according to package instructions and pour the batter into the pan.

In a mixing bowl, combine creamy peanut butter and softened unsalted butter. Beat until fluffy, about 4–5 minutes.

Add light brown sugar, granulated sugar, eggs, and vanilla extract to the butter mixture and mix for about 4 minutes until smooth.

In a separate bowl, whisk together flour, baking soda, and salt. Fold in oats and chocolate chips.

Fold the dry ingredients into the wet mixture until just combined, then drop spoonfuls over the brownie base.

Sprinkle Halloween decorations over the batter.

Bake for 25–30 minutes and check for doneness with a toothpick; let cool for at least 30 minutes.

Prepare frosting by beating together butter, confectioners' sugar, vanilla extract, and heavy cream until creamy. Add food coloring if desired.

Once brownies are cooled, pipe frosting over the top and add candy eye decorations.

Slice into squares and serve at your spooky celebration.