Herdy Gerdy

Cheat mode
Press L2, L1, L2, L1, Up, R1, R2, R1, R2, Down, Select at the title screen.
If the codes are accepted, the screen will fade out a few seconds.
Press Start and - you can access to the new options in the main menu.

Stop Gromps From Chasing You:
When a Gromp is chasing you, jump in to a pen.

Unlockable secret options:
Collect the indicated ammount of bells on the indicated level, then give
the Cowbell to the cow herder in Meadow Village to unlock secret
options at the extras screen:

Hidden 1 Option - Gerdy's Concept art:
Collect 100 Bells in the Gerdy's Hut level herder

Hidden 2 Option - development movie sequences:
Collect 100 Bells in the Meadow Village level

Hidden 4 Option - Unused level designs:
Collect 100 Bells in the Beaver Creek level

Hidden 5 Option - Concept art:
Collect 100 Bells in the Moonlit Peaks level

Hidden 6 Option - Gerdy's Concept art:
Collect 100 Bells in the Goldmine Gorge level

Hidden 7 Option - Concept art:
Collect 100 Bells in the Belders Spring level

Hidden 8 Option - Concept art:
Collect 100 Bells in the Belders Spring level

Hidden 9 Option - Tomb Raider: Angel of Darkness screenshot:
Collect 100 Bells in the Ancient Temple level

Hidden 10 Option - Wireframe animation:
Collect 100 Bells in the Pirates Cove level

Hidden 11 Option - Background concept art:
Collect 100 Bells in the Skrags Nest level

Hidden 12 Option - Gerdy wireframe animations:
Collect 100 Bells in the Elven Wood level

Hidden 13 Option - Box art concepts:
Collect 100 Bells in the Forest Glade level herder

Hidden 15 Option - wireframe animations:
Collect 100 Bells in the Crystal Lake level herder

Hidden 17 Option - unused level concepts:
Collect 100 Bells in the Crystal Lake level herder

Hidden 18 Option - Concept art:
Collect 100 Bells in the Foxtown Bridge level

Hidden 19 Option - Concept art:
Collect 100 Bells in the Foxtown Docks level

Hidden 20 Option - Sadorf concept art:
Collect 100 Bells in the Tournament Island level