There's a few single player modes:
- Free Play: Open-ended mode where you're just trying to keep your people
happy and grow your population.
- Scenarios: Short little "missions" where you're trying to achieve a goal in
a certain amount of time (or some other condition).
- vs CPU: Make it to 100,000 people first, or destroy the other island to win.

If you have SRAM on your GBA cart you can optionally save a replay of the game
to the SRAM when you quit from the pause menu. Replays can be replayed from
the Single Player menu. Similarily, you can also save your game from the Pause
Menu and load from the Single Player menu later.