DUKE NUKEM: TIME TO KILL  

Enter all codes while game is paused 

Invincibility:          L2,R1,L1,R2,Up,Down,Up,Down,Select,Select
All weapons:            L1,L2,Up,L1,L2,Down,R1,Right,R2,Left
Infinite ammo:          (Left,Right,Left,Right,Select)x2
Powered up weapons:     Right,Right,Left,Right,Right,
                    Left,Right,Right,Left,Select
Double damage:          (L2,R2)x5
Invisibility:           (L1,R1)x5
Level select:           Down(x9),Up
All items:              R1(x5),L2(x5)
All keys:               Up,Right,Up,Left,Down,Up,Right,Left,Right,Down
Big head Duke:          R1(x9),Up
Small head Duke:        R1(x9),Down
Big head opponents:     R1(x9),Left
Small head opponents:   R1(x9),Right 


These are all the secrets i have found in 2p mode

collosium- to get the jetpack go over to the first wall after you go
through the doorway- climb it and go through the wall to collect the
buffolo rifle and jetpack.

castle-to get a rpg go to the corspes hanging on the wall and press x to
climb into a hidden wall

mesa- go to the room with only ane dynamite, turn right when you get
there. gewt close to the wall and press x.

.... i am trying my best to find out the level secrets for dingeon,
factory, and warehouse.