Use a butter knife to cut the brownies into about 72 square-inch cubes. Prepare strawberries by slicing with a knife; cut marshmallows in half with kitchen shears. On a bamboo skewer, slide a brownie piece, two blueberries, a marshmallow half, and a strawberry slice. Continue this step one more time, adding a final piece of brownie to the top of the skewer.

Repeat with remaining ingredients. Makes about 24 skewers.