When you complete ALL the Akumpa Ruins levels Antartica Temple will become unlocked, to unlock this feature for ALL the characters you must view the True Ending.
Change character's color
Collect four golden skulls.
Commander Video
Collect 6 golden skulls.
Easy 'Serpentine' Achievement
The Key of Serpentis can be found near the exit door in level 2-1. You will only be able to access it after unlocking Antartica and when using Aban Hawkins.
Easy 'Stone Cold' Achievement
You can get this Achievement easily by obtaining the key of Serpentis to unlock the final stage and Boss and then Killing that Boss.
Pokemon reference
Complete World 1 and watch the video sequence. Aban will talk about the temple of Poko-mum and refer to it as "Pocket Monster", which is the Japanese title for the Pokemon series of games.
Tower of Nanar cooperative mode
Collect 5 golden skulls.
Unlock Bonus Characters
The following characters become unlocked when you complete the corresponding task.
Commander Video:
Collect 8 golden skulls.
Sugimoto:
Collect 16 golden skulls.
Juni:
Collect 18 golden skulls.
President Thompson:
Collect 20 golden skulls.
Zombie:
Collect 23 golden skulls.
El Testigo:
Collect 26 golden skulls.
Curly Brace:
Collect 30 golden skulls.
Jim Hawkins:
View the 'True' ending.
Tina Hawkins:
Successfully complete Ukampa Ruins.
Unlock Counseil's Duty Free Shop
Counseil's Duty Free Shop will become unlocked when you have collected 12 golden skulls.
Unlock Tower Of Nanar Co-Op Mode
This feature will become unlocked when you have collected 6 golden skulls.
Various Achievements
Complete the following achievements to unlock Xbox Live Gamerscore points.
Achievement
How to unlock
Collector (200 points)
Unlock every character and costume.
Finish the Fight (50 points)
Unlock Space Marine Aban.
Golden Boy (100 points)
Complete the Golden Temple.
Headhunter (100 points)
Collect all golden skulls.
Lost and Found (50 points)
Complete the Lost Levels.
Serpentine (50 points)
Find the Key of Serpentis.
Sold Out! (150 points)
Purchase every unlockable in Conseil's Duty Free.
Speed Runner (50 points)
Complete every stage of the main game as Aban Hawkins with a cumulative time of less than 30 minutes.
