In a large bowl, use an electric mixer to combine the butter and sugars until light and fluffy, about 2 minutes. Bean in the vanilla until combined. Beat in the eggs, one at a time, on medium-low speed until just combined, about 30 seconds.
In a medium bowl, whisk together the dry ingredients: all purpose flour, cake flour, baking soda, baking powder and kosher salt. Gradually add this to the butter mixture, beating on low speed until combined, about 2 minutes. Stir in the M&M's pretzels, chocolate chips and marshmallows with a wooden spoon. Cover, and chill for at least an hour (or overnight).
Preheat the oven to 400℉. Line baking sheets with parchment paper.
Remove the dough from the fridge. Scoop dough about 2 tablespoons and roll into a ball- arrange 2-inches apart on a prepared baking sheet. Keep dough refrigerated, while prepping. Bake until edges are golden, 10-12 minutes. Remove from the oven, and top immediately with sea salt. Cool on baking sheets for a few minutes, then transfer to wire racks to cool completely.