You can buy the combination tickets which include the ticket of Ocean Park, a New Territories Day Pass, and two airbus coach tickets. You walk from the Regal Riverside Hotel to Sha Tin Wai Station and buy this combination tickets there. Use the New Territories Day Pass to enter the station, reach Tai Wai and take the East Rail and get off at Hung Hom Station, take the Exit C, and use the airbus coach to Ocean Park. Good trip!