Easy Star in Jolly Roger Bay
Go to the first mission of Jolly Roger Bay. You must have Mario to do this. From the starting point, there should be some of those orange brick blocks near you. Destroy them, and get the Shell that's inside. Take the shell out onto the water, and look at your map.Surf over to the ship (The dark circle with the star over it), and when you get there, try to jump off of your shell. (I think you jump and press R in the air.) You should land back on the water and then fall under the surface. Swim down and let the eel come out of the door. Then, go inside the boat. You will be underwater and a Treasure chest will be there. DO NOT TOUCH THE TREASURE CHEST YET! First, swim up to the other end of the room and get some air. Then, swim back to the treasure chest, but turn twoards the star. Now, swim at the treasure chest, and swim as fast as you can twoards the star. Hopefully you will land on a high ledge. Now, you can either jump to the top ledge, (hard) or crawl up the hill. (Easy but slow. If you hit a high ledge, it makes this a lot easier and quicker.) Now, open the box, and get the star inside.