These become unlocked in the 'Extras' menu when you complete the indicated secret mission.

Unlock Introducing Blob:
Complete 'Leaps of Faith'

Unlock Pre-Production Trailer:
Complete 'Top of the World'

When the following tasks have been completed the corresoponding entry in the 'Galleries' option at the 'Extras' menu will become available.

Unlock Gallery Blob:
Complete the 'Seaside Roller' secret level.

Unlock Gallery Revolutionaries:
Complete the 'Ship To Ship' secret level.

The following secret missions become available when you complete the corresponding task.

Unlock Miles O Silos Mission:
Beat The Docklands

Unlock Seaside Roller Mission:
Beat Last Resort

Unlock Ship to Ship Mission:
Beat Uptown

Unlock Sizzle Race Mission:
Beat Downtown

Unlock Hill Climb Mission:
Beat Ministry of Ink

Unlock Jetbike Blitz Mission:
Beat Guggentraz Island

Unlock Factory Run Mission:
Beat Chroma City Fun Park

Unlock INKT Acedemy Mission:
Beat The Chroma Dam

Unlock Billboard-O-Rama Mission:
Beat Hanging Gardens

Unlock Sinking Feeling Mission:
Beat Lake Raydia

Unlock Tower of Power Mission:
Get a Gold medal for Lake Raydia

Unlock Trainspotting Mission:
Get a Gold medal for Guggentraz Island

Unlock Blob Smash Mission:
Get a Gold medal for Chroma City Fun Park

Unlock Crane Fighting Mission:
Get a Gold medal for The Chroma Dam

Unlock Trainspotting Mission:
Get a Gold medal for Guggentraz Island

Unlock Deep Down Mission:
Get a Gold medal for Ministry of Ink

Unlock Forgotten Forest Mission:
Get a Gold medal for The Docklands

Unlock Inky Canyon Mission:
Get a Gold medal for Hanging Gardens

Unlock Leaps of Faith Mission:
Get a Gold medal for Uptown

Unlock Lost Freeway Mission:
Get a Gold medal for Downtown

Unlock Top of the World Mission:
Get a Gold medal for Last Resort

When you complete the indicated task the corresponding mission will become an available option.

Unlock 'Seaside Roller' Mission:
Beat 'Last Resort' mission.

Unlock 'Ship to Ship' Mission:
Beat 'Uptown' mission.

Unlock 'Sizzle Race' Mission:
Beat 'Downtown' mission.

Unlock 'Leaps of Faith' Mission:
Get a Gold medal for 'Uptown' mission.

Unlock 'Lost Freeway' Mission:
Get a Gold medal for 'Downtown' mission.

Unlock 'Top of the World' Mission:
Get a Gold medal for 'Last Resort' mission.

Unlock Invincibility:
Durning gameplay hold C and press 1 four times (to disable the effect repeat the code).

Unlock Multiplayer Options:
Hold C at the starting menu and press 2 two times, B two times, 1 two times, B two times.

Unlock ALL Moods and Music:
Hold C at the starting menu and press B two times, 1, 2, 1, 2, B two times.

Unlock Extra Lives
During gameplay hold C and press 2 two times, 1 two times, 2 two times.

Unlock 10 Extra Minutes:
During gameplay hold C and press 1, 2, 1, 2.