Unlockable Bonus Level 
Beat the game once. 

Unlockable:         How to Unlock:
Bonus Level         Finish the game one time. 


Unlockables 
Defeat the following bosses. 

Unlockable:         How to Unlock:
Inferno             Beat Colossus 
Judgement           Beat Enforcer 
Neutron Gun         Beat the boss on level 30 
Onslaught           Beat the boss on level 10 
Trident             Beat the boss on level 60 
Vulcan              Beat the boss on level 20 
Blast Helm          Beat Enforcer 
Surge Helm          Beat Mantin