Prepare the Pan: Line a 9x13 inch baking pan with parchment paper, leaving an overhang on two sides for easy removal. Alternatively, grease the pan lightly with butter.

Melt Butter and Marshmallows: In a large saucepan, melt the butter over low heat. Add the entire bag of mini marshmallows and stir continuously until completely melted and smooth.

Add Flavor: Remove the saucepan from the heat. Immediately stir in the vanilla extract and salt.

Combine with Cereal: Quickly add the 6 cups of Rice Krispies cereal. Gently fold until every piece of cereal is thoroughly coated in the marshmallow mixture.

Press into Pan: Transfer the mixture to the prepared pan. Using a sheet of parchment paper or buttered hands, gently press the mixture into an even layer. Avoid over-packing to keep the treats soft.

Cool and Set: Allow the treats to cool and set completely at room temperature for at least 1-2 hours.

Cut and Decorate: Once set, use the parchment paper to lift the entire slab from the pan. Cut into squares or use Halloween-themed cookie cutters to create shapes. Decorate with melted chocolate, sprinkles, and candy eyes as desired.