Codebreaker master code for Ico is
9A7C5BED 18AB858F
To have not too smart AI characters use this codebreaker code
2AAB3714 03E00008
2A973714 00000000
2A733D40 03E00008
2A7F3D40 00000000
Press L1+Select, to save your game first you need the code below which is:
DA77D007 B25F884B
1A8573A1 0000001C
Use this code along with pressing R1+ select while playing Ico
The codebreaker code is:
EA5983A1 9828D6F5
2A933EE4 03E00008
2A9F3EE4 00000000
Use R2+ Select to walk normal.
EA5983BB 9828D6EF
2A933EE4 27BDFF70
2A9F3EE4 8F83A418