I explained it in first post:
1. After Alien Flying Troopers you'll reach the boss fight, he is damaged and then will rise from the ground, the game saves so the boss fight begins. Proceed normally without any cheat.
2. Exit the game to main menu ( YOU MUST EXIT THE GAME ) go to extra, activate the Invincibility cheat.
3. Reload the checkpoint by selecting continue the campaign.
4. Defeat him on the first phase he will go down and begin pulling your cart towards himself, wait until game saves then Exit to main menu.
5. Reload the checkpoint by selecting Continue the campaign ( you don't need to deactivate the cheat)
6. Finish him off Fast ( this part you dont have any active cheat )
7. Finish the Level
If i die at point 6, does it still count?
English is not my mother-language...