Preheat oven to 350°F and grease an 8x8-inch pan.
Mix cocoa powder, flour, salt, and baking powder in a bowl.
In a large bowl, combine melted butter, sugar, eggs, and vanilla.
Fold in dry ingredients and chocolate chunks until just mixed.
Pour batter into prepared pan and bake for 30 minutes.
Cool completely, then cut into 9 squares.
Line a surface with parchment paper and place brownies apart.
Melt orange candy melts as directed.
Dip marshmallows into melted candy, then place on brownies' centers.
Tap brownies gently to smooth coating.
Add chocolate chips on marshmallows for pumpkin stems.
Let the candy coating set for 30 minutes.
Melt remaining chocolate chips and pipe faces on brownies.
Allow faces to harden for 15 minutes.
Store in an airtight container for up to 3 days.