Bake your favorite brownie recipe in a 9x13-inch pan and let it cool completely. Pop the pan in the fridge for at least an hour so the brownies firm up. Once chilled, slice them into 1-inch cubes using a sharp knife for clean edges.
While the brownies chill, rinse your strawberries and blueberries under cool water. Hull the strawberries and pat everything dry with a paper towel. Dry fruit sticks better to skewers and keeps the brownies from getting soggy.
Take a skewer and start alternating pieces: a brownie cube, a strawberry or a few blueberries, a marshmallow, and repeat. Keep going until the skewer is comfortably full, leaving a small handle at the bottom for gripping.
Continue threading the remaining skewers the same way, mixing up the pattern so each one looks a little different. This keeps the platter visually interesting and lets everyone grab their favorite combination.
Warm your hot fudge or chocolate sauce slightly so it flows easily, then drizzle it generously over the finished kebabs. Use a spoon and move it back and forth for that classic bakery-style zigzag look.
Place the assembled kebabs on a platter and refrigerate them until you're ready to serve. This keeps the marshmallows and brownies firm and makes the whole platter easier to transport if you're heading to a party.