Super Mario Sunshine Glitches

Walk Underwater in Isle Delphino 2
Start a new game and collect the first shine at the airport. Now you
should be take to Isle Delphino, near the centre of the island you
should find some barrels, grab one and take it to the beach area. Walk
down the beach until you reach the point where Mario is just about to
start swimming, now drop the barrel, push forward slightly and Mario
should start swimming, now tap b and you should grab the barrel and be
standing underwater! Now run around as much as you want.