Level select:
To unlock all levels, at the main menu, press Up, Left, Up, Left, Down, Right, Start.
Stewie’s weapons:
Unlock the following weapons by collecting the corresponding numbers of parts and combining them:
Heat Seeking Warheads – Collect 700 Parts
Hyper Plasma Ball 1 – Collect 300 Parts
Hyper Plasma Ball 2 – Collect 400 Parts
Plasma Artillery 1 – Collect 200 Parts
Plasma Artillery 2 – Collect 300 Parts
Plasma Ball 1 – Collect 100 Parts
Plasma Ball 2 – Collect 200 Parts
Rocket Launcher 1 – Collect 500 Parts
Rocket Launcher 2 – Collect 700 Parts
Shock Wave 1 – Collect 400 Parts
Shock Wave 2 – Collect 500 Parts
Spread Shot 2 – Collect 100 Parts