With the small brush, mix in the plate blue with a tiny bit of black. Start from the side and draw a mountain that goes from the left to the right. Be creative, it can be small or big. Once you draw an outline of a mountain you like, fill it in with that dark blue color you mixed.
With the same rinsed small brush, dip it in white, and paint a coin sized moon on the top left. And lastly, with barely any white paint on the brush and very light pressure, draw random lines in the water to add some reflections.
Optional: You can then also use the small brush with some white paint to stamp some water splashes around the dolphins tail.