For the feta skewers, cut the feta and the watermelon into similarly sized cubes, 18 of the watermelon and 12 of the feta.
Assemble ingredients on each skewer in this order: watermelon, mint, feta; repeat the pattern and then cap each skewer with an extra piece of watermelon.
For the mozzarella skewers, use a melon baller to make 18 melon balls close in size to the mozzarella.
Assemble ingredients on each skewer in this order: melon, basil, prosciutto; repeat the pattern and then cap each skewer with an extra piece of melon.
Arrange the skewers on a platter and drizzle liberally with olive oil, splashes of balsamic, and a few twists from your black peppercorn grinder.