Preheat your oven to 350°F (175°C).

Prepare the yellow cake mix according to the package instructions, combining it with eggs and water.

Pour the batter into a greased 9x13 inch baking dish and bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.

Once the cake is done, remove it from the oven and let it cool in the pan for about 10 minutes.

Using the handle of a wooden spoon, poke holes all over the top of the cake.

In a separate bowl, mix the sweetened condensed milk with the mixed berries, then pour the mixture evenly over the cake, ensuring it seeps into the holes.

Let the cake cool completely at room temperature, then refrigerate for at least 2 hours to allow the flavors to meld.

After chilling, spread the whipped topping evenly over the cake.

Garnish with the sliced strawberries, blueberries, and raspberries on top, and add mint leaves if desired.

Slice and serve chilled, enjoying the refreshing taste of summer in every bite.