HEre are the codes:

At Mt. Moon take a picture of the purple mist. When it develops it will be a picture of a Gastly, Haunter or Gengar.

Game Shark Codes

---------------- Enable Code (Must Be On) DE000400 0000 F103D8A0 2400

Unlock All Levels 810C2212 0006

Have Apple 803AE51F 0001

Have Apple & Bomb 803AE51F 0002

Have Apple, Bomb & Flute 803AE51F 0004

Stop Beach Level* D00489E1 0020802020F5 0001

Stop Tunnel Level* D00489E1 0020801DDC55 0001

Stop Volcano Level* D00489E1 0020801FC5C5 0001

Stop River Level* D00489E1 0020801EF96D 0001

Stop Cave Level* D00489E1 002080202225 0001

Stop Valley Level* D00489E1 0020801D9ABD 0001

* - Press L to stop the level and Start to continue the level again.