Preheat the oven to 350°F and line two baking sheets with parchment paper.
In a mixer, cream the butter and both sugars until light and fluffy, about 3 minutes.
Add eggs and vanilla and mix.
Mix in flour, baking powder, baking soda, and salt. Add pretzel pieces, peanut butter chips, and marshmallow bits. Mix well.
Using a cookie scoop, drop dough balls onto the baking sheet, spacing them out about 2 inches apart.
Bake for 12 to 15 minutes, or until the cookie edges are brown. Cool on the baking tray for 10 minutes. Then transfer to a wire rack to cool completely, about 30 minutes.