Preheat the oven to 350. Grease an 9'x13' pan and line with parchment.
In a medium. bowl, whisk the flour, salt and baking powder.
In a large bowl using a hand mixer or the bowl of a stand mixer, cream butter and sugars until fluffy. Beat in the eggs, one at a time. Add the vanilla extract and combine.
Add flour mixture to butter mixture in two batches. Using a wood spoon, fold in the Halloween candy.
Transfer the batter into the prepared baking pan and, using wet hands, spread it evenly. Top with sprinkles and 1/4 cup colorful candies like M&M's or Smarties. Place it in the refrigerator for 10 minutes.
Bake in the oven for 30 minutes or until edges are golden brown. Allow to cool completely before cutting into bars.