Thunderstrike - Platform: Playstation 2

Level Select 
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Set the Vibration level in options to 1 and both 
SFX and Music to 0. 
Then hold L1 + L2 + R1 + R2 + Circle + Square. 
A message will confirm you have done it right. 

Ending bonuses 
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Successfully complete the game under the hard difficulty 
setting. The maniac difficulty setting and a bonus chopper 
and will now be unlocked. 
The bonus chopper flies, turns, climbs, descends, 
and shoots faster.