I loved Platinum for a lot of reasons, and one of them was the access to so many new Pokemon, like your challange, Moai the Nosepass. This particular Nosepass loves the tropics, and constantly wants to visit the beaches of Sinnoh. As a result, Nosepass refuses to evolve, until you take him to three unique beaches. To prove he is the king of the beach, solo Volkner who resides in the greatest beach town of all, Sunyshore.
Sinnoh Beaches: Route 213, Route 219, Route 220, Route 221, Route 222, Route 223, and Sunyshore City.