Place marshmallows in the refrigerator or freezer to chill. (At least 30 minutes) Put a piece of parchment paper in the bottom of an 8x8 or 9x13 pan leaving ends out to remove. Combine the butterscotch chips, peanut butter, and butter in a large saucepan. Cook over low heat until the mixture is melted and smooth. Remove from the heat and allow to cool slightly. Add in coconut and vanilla. Stir until combined. Fold in the marshmallows. Pour into baking pan spreading evenly with a spatula. Refrigerate for 1 hour. Remove the bars from the pan (lift parchment paper) and cut. Keep refrigerated or freeze.