All of the above solutions are great, and I used them for the most part, however, this is a very frustrating difficulty with terrible load times. Therefore, I wanted to spend as little time as possible on this. After browsing the PlayStation forum tagged below, I learned of a way to get through most of the game by tricking the game into letting you use invincibility. It's worked for me so far, and I'll post updates as I progress.
The main strategy is to move through the game using the chapter select, obviously on Damn, I'm Good. Play through the level as normal, until you get to a place where you are having trouble, or die, then follow below:
1. Quit to the main menu
2. Activate Invincible, on the cheat menu. (Instagib and Infinite Ammo also work)
3. Continue campaign
4. Play to the next checkpoint
5. When you see the Duke Nukem saving icon in the bottom right corner of the screen, pause and quit to the main menu
6. Select continue campaign (this automatically turns off any cheats)
7. Continue as normal
NEVER TURN ON CHEATS IN THE IN GAME MENU, ALWAYS USE THE MAIN MENU
If you have trouble in consecutive sections, you can use the above trick as many times in a row as you want, just make sure that when it saves the first section, back out then come back in with no cheats, then back out to turn them on again. Tedious, yes, but faster than dying 20 times in a row.
There are some tricky parts or how to go between sections on multi part levels that I'll detail below.-Mothership Battle
- Wait until the game saves as a drop ship picks up some enemies, then do steps 1-3 above. After the short "4 hours later" cut-scene, it should save. Quit to the main menu and click continue campaign.-The Lady Killer Part 2
- Following the steps outlined above, I used the trick for the section after you are brought back to regular size, as well as a couple rooms along the way. The last room of this section has a checkpoint before it loads part 3, so feel free to use the trick if you get stuck anywhere in here.-The Lady Killer Part 3
- Relatively easy, however the only hard part is the last fight after you climb the statue and go through the duct work. there is no checkpoint after the fight before the level ends so I think the only way to do this is legit.-Vegas In Ruins
- There's a hard part that takes up two checkpoints: when you first go into the pit with the Battlelord, and when you actually fight the Battlelord. Use invincibility if you need to, as there is a checkpoint right after killing the Battelord-The Duke Dome Part 1
- The main part I used it on was in the construction trailer where you turn the power on. There is a lull in the action (before the pig cops flip the trailer) where it saves. There is no checkpoint between this and part 2. The trick is after you open the fence and walk forward a couple steps, the screen will fade to black. While it's doing this, press pause and you'll notice that it is saving. Go to the cheat options from the pause menu and turn it off, then unpause, and it will continue to part 2.-Queen Bitch
- After you kill her, it goes into a cutscene. Once it starts fading out, press pause and there should be a save icon. Quit out and you shouldn't even have to load it back up. If you look at Chapter Select, it should be done.-Crash Course
- Once you get on the machine gun, it saves. Do the above steps. The save point is as you leave the machine gun. Back out, and continue campaign like normal.-Duke Burger Part 3
- The rooftop battle is hard. I used cheats in every section. Remember to turn them off at every checkpoint, go back into the game, and then quit out to turn them back on. After you get in the dropship at the end, keep your finger on the pause button. When the screen is fading, and the save icon comes up, pause and quit out. Boom. You don't even have to go back into the game, as it's already complete.-Dam Top
- I've heard this is a really hard one to get the trick done on, so I beat it legit using LAFTAs solution on this page. However, when I rappelled down to the base of the dam, and went into the door and down the stairs, I saw a save point, so I'm almost certain the trick will work here. It's a very short level so if it doesn't work, you didn't waste much time, and the Battlelord fight is actually very easy.-The Forkstop Part 1
- Turn on cheats for the Ocktaking fight, just turn it off after the fight via the pause menu, as the checkpoint loads Part 2.-The Forkstop Part 2
- The last fight is hard, so turn it on. There's no checkpoint between this and the end of the level. When in the elevator at the end, when it starts to save, quit the game. On the Chapter Select, it should now be complete.-Generator Room
- On the Octaking fight, after you kill him the first time, quit and turn off the cheats. Then the second part is very easy.
It should save after talking to the president, and him getting killed. Do the above steps. After you get the health bar down the 3rd time and kill the boss, it should save again. This is your cue to back out and continue campaign
Guide that helped me.https://www.playstationtrophies.org/forum/duke-nukem-forever...