Mix together instant vanilla pudding and 4 cups milk (or follow package instructions). Whisk together until no lumps remain and refrigerate until set.
Meanwhile prepare your sand. Remove cream from the oreos and add cookies to a food processor. Blend until fine grained sand, and set aside.
Optionally, create your water. You have two options here, add drops of food coloring to the entire tub of whipped topping and mix to make a solid blue color. Or, reserve roughly a ½ - 1 cup of whipped topping and add drops of blue food coloring to swirl in blue food coloring for a tie-dye look.
Assemble your cups. Layer pudding, then whipped topping, then pudding until cup is mostly full. Leave roughly 1" at the top. Add a layer of oreo "sand", making sure to leave at least ½" at the top for your scene. Repeat for all 10 cups.