Unlock the following bonus options at the "Options" menu by performing the corresponding tasks:

OPTION - HOW TO UNLOCK
Equipment Strength Upgrade - Collect all 103 illustrations for Tobin's Spirit Guide.
Faster Health Recovery - Collect 50% of the illustrations for Tobin's Spirit Guide.
Gozerian Rookie Outfit - Beat the game on the Gozerian difficulty. This outfit will allow you to be immune to sliming.
Increased Scanning Speed - Scan 50% of the ghosts and scannable objects for Tobin's Spirit Guide.
Invulnerability - Beat the game with all 103 illustrations collected and scan all 103 ghosts and scannable objects.
No Equipment Overheat - Scan all 103 ghosts and scannable objects for Tobin's Spirit Guide.