To enable cheat mode press V + T + S. 
 Next, enter one of the codes below to 
 activate the following cheat function.
 
 Function                         Code
 Additional weapons             - A + R + K 
 Free movement                  - B + Y + Z 
 Invincibility                  - E + L + K 
 Press F3 to jump to next world - O + M + R 
 Full database                  - R + Y + 1