Butter a 9X13 inch baking pan. Line with parchment, allowing a 2 inch overhang on the longer side. Brush parchment paper with butter (you do not need to brush the overhang).
Whisk together flour, baking powder, and salt in a bowl. Using a wooden spoon, mix butter and brown sugar in a medium bowl until fluffy, about 2 minutes. Add eggs and vanilla; mix until well combined. Mix in flour mixture until combined. Fold in half of each of the marshmallows, chocolates, butterscotch chips and caramels.
Spread batter in prepared pan. Scatter remaining marshmallows, chocolates, butterscotch chips, and caramels on top, bake until top is golden brown and a cake tester inserted in center comes out clean, about 35 minutes. Let cool on a wire rack. Lift out of pan, and transfer to a baking sheet. Refrigerate until set, at least 30 minutes.
Remove parchment, and cut into 16 triangles. Bars can be stored in an airtight container for 1 week.