Metal Slug X [PSX]

Mission select
Successfully complete arcade mission mode to unlock mission select in arcade mission and another mission modes.

Chat mode
Select Combat School and while it is loading, rapidly press Square until the menu appears. The instructor will ask if you want to chat with her.

Combat School rankings
Rank Points
Super Devil 1000+
General Of Army 990+
Lieutenant General 890+
Major General 780+
Brigadier General 700+
Colonel 650+
Lieutenant Colonel 600+
Major 575+
Captain 560+
1st Lieutenant 550+
2nd Lieutenant 500+
Chief Warrant Officer 475+
Warrant Officer 450+
Sergeant Major 425+
Master Sergeant 400+
Sergeant 1st Class 350+
Staff Sergeant 300+
Sergeant 250+
Corporal 200+
Private 1st Class 150+
Private 100+

Game Shark Codes
Infinite Lives 80047522 2400
Infinite Bombs 800398BE 2400
Infinite Arms Ammo 8002DCE6 2400
Infinite Time 8002962A 2400
Infinite Vehicle Health 80053F7E 2400
Invisible P1 800CA30C 0068
Extra Prisoners P1 800879EC 00FF
Max Score P1 800EE290 FFFF
Invisible P2 800CA458 0068
Extra Prisoners P2 800879F0 00FF
Max Score P2 800EE298 FFFF