Super Mario Sunshine Cheats

Unlimited Lives and Coins in Plaza
For unlimited lives:
There are two one-up mushrooms in the Plaza that will re-appear after you save and exit or enter and exit a level. Simply keep going back to get them:
1. On the way to the red cannon to fire you to the theme park there is manhole cover on a small platform, fall down the right hand side and swim down between the two platforms for a one-up mushroom
2. Go to the beach near the lighthouse tower, where there are two parasols up on the beach walk around, you will see a manhole cover shape as you walk over it. It is covered by sand. Jump and press L to slam down the sewers and get another one-up mushroom

For unlimited coins:
Collect all the coins you can find scattered around the plazza, especially in the sewers. When you have as many as you can find, enter one of the secret levels (e.g. down the green pipe near the light house or turbo nozzle through the doors to the 'prison', or somersault off the boat up where the floating coin is for the pinball secret level). Press start and exit the secret level, you will have retained all the coins you collected and they will have reappeared. Repeat, 50 coins gives you a one up and 100 coins makes the Plaza's secret shine appear.