Level Select has just released the Super Mario Eclipse Mod for Super Mario Sunshine. This is basically a romhack and you can run it on PC via the Dolphin Nintendo GameCube emulator.
As Level Select noted:
“Super Mario Eclipse is part beta restoration, part enhancement, part original mod, and all fan service. With dozens upon dozens of new missions, fully custom worlds, challenging secret courses, and an interconnected Isle Delfino to boot, this is the Super Mario Sunshine experience you always wanted- and then some!”
The game now has new secrets, and supports multiple playable characters. Furthermore, it presents an all-new expanded story, crazy new gimmicks, exciting new moves and abilities, and references to your favorite Gamecube era Mario Games.
Now I don’t know whether Nintendo will attempt to take down this fan project. Nevertheless, and as always, I recommend downloading it while you still can. Do note though that this is the first public demo and not the final/full version.
Below you can also find a new trailer for this mod.