Create a series of black and white illustrations for a kids' coloring book in a cartoon style. The theme is 'Dragon and Mythical Beasts'. Each page should feature different underwater scenes with cute, smiling sea creatures like fish, turtles, octopuses, and dolphins, as well as elements like coral reefs, seaweed, and treasure chests. Ensure the outlines are clear and bold for easy coloring. The overall tone should be playful and fun, with characters showing friendly expressions and engaging in light-hearted activities like playing, exploring, and interacting with each other.