Level select - energy gain
When the credits are shown when you turn the game on press left,up,X,up,right,Y It will take you to a cheat screen then press Y+A and then press X+B.

Level Codes
Level 2 - QBGB
Level 3 - VPFD
Level 4 - CPRY
Level 5 - FCWZ
Level 6 - RLFJ
Level 7 - CBBY
Level 8 - TDYT
Level 9 - KKBG
Level 10 - VYRX
Level 11 - CNRN
Level 12 - CRQF
Level 13 - DXHG
Level 14 - QBTV
Level 15 - TMKT
Level 16 - VMTB
Level 17 - XCWV
Level 18 - TQZH