Now that the police have released you, you are free to roam the area. Immediately, you'll notice a D.E.B.S. Alert at the bottom of the screen, telling you that some people have gone missing in Bianco Square. Head straight over there by following the path in front of you. You'll notice Toadsworth and Peach when you reach the corner - Peach is already complaining and wants to go home! You'll then be shown another huge pile of goo in Bianco Square, so get over there and start spraying.
The second Gate Keeper
Spray the large pile of brown goo to awaken another Gate Keeper monster, and take him out just like before (spraying him in the mouth with the FLUDD). This time when you've defeated the monster someone new will appear; it's Shadow Mario!
The chase
After Shadow Mario grabs Peach and runs off you have to chase him around town and keep spraying water at him. Start by running over to where Peach and Toadsworth were standing and when you see him start spraying him and then just keep chasing and spraying him until he gives up. Don't worry if you lose him for a while as he'll kindly stop and wait for you to catch up. When you've sprayed him enough he'll fall over and drop Peach, so just run over to them. Peach is now safe but you need to spray Shadow Mario a few more times.
Eventually he'll head back to Bianco Sqaure for one last spraying, and then he paints a mysterious "M" on the platform of the statue. Spray the "M" with water and it will glow and become a portal for Mario to jump into. So go ahead, jump in and be transported to Bianco Hills.
Finding Ricco Harbor
After completing chapter 1 of Bianco Hills, you will be able to unlock a new area; Ricco Harbor. To do this, head west from the Bianco Hills portal until you reach a pier covered in black goop. This is another Gate Keeper, so spray the big blob to reveal him and sort him out in the normal way. Once you've defeated him, the boathouse appears with a rainbow coloured portal on it. Spray the portal to activate it, and you can now enter Ricco Harbor.
Finding Gelato Beach
After completing chapter 3 of Bianco Hills, you'll be shown a big puddle of goop where the lighthouse used to be. To and find it from Bianco Square, head to the right and follow the beach until you get to the goo-covered platform. Spray the goo to reveal yet another Gate Keeper. Defeat him in the usual way to restore the lighthouse, then be a good man and clean off poor little toad before spraying the new portal to activate it. This can now be used at any time to enter Gelato Beach.
Finding Pinna Park
If you go to the red cannon by the ocean at this point you'll be able to unlock the Pinna Park area. To find it, from the portal in Bianco Square go ahead and left, past the palm tree and between the 2 buildings up the little hill. At the top of the hill use the hover nozzle to get over the river the the lower path ahead. Now go forward and through the big archway on your left to find the cannon. After the cut-scene where Shadow Mario kidnaps Peach (again) you can now jump into the red cannon to be launched over the sea to Pinna Park.
For now, these are the only areas you can unlock, until you complete a few more episodes.