Empty the 12-ounce jar of marshmallow spread into a large bowl. Add 5 ounces each potato chips and pretzels into the marshmallow-spread mixture. Mix the chips into marshmallow spread until thoroughly incorporated. Add the rest of the chips and pretzels and stir until all chips are incorporated into mixture.
Line a 9-by-13-inch baking pan with parchment paper, making sure that some parchment hangs over the sides. Place marshmallow mixture into parchment and let the mixture set for two hours. Once the bars have set, cut them into 6 equal squares.
In a microwave-safe bowl, heat up 4 tablespoons of Nutella and drizzle some over each bar. Serve.