When you complete the game on any difficulty setting the option to activate cheats will become unlocked at the bonus menu. These cheats include 'Slow Motion' and 'Infinite Ammo'. Note: unlike in many other games enabling cheats will NOT disable earning any trophies.
Unlock ALL Weapons:
Completing the game on any difficulty setting will unlock ALL the weapons in the game at the 'Bonus' menu.
Barrok .44 Pistol:
You can find the Barrok .44 high caliber pistol the first time in Chapter 8, Scotland. Although this weapon has a slow rate of fire it is able to do high damage and almost always kills with one-hit. This weapon can also be unlocked at the 'Bonus' menu when you complete the game on any difficulty setting.
Unlock Final Boss and Game Ending:
When you have beaten the game on the Crushing difficulty setting you will earn the 'Charted! – Crushing' trophy and be able to view the ending cutscene and final boss epilogue. To make getting this trophy easier enable cheats in the 'Bonus' menu. Note: you need to beat every single chapter on Crushing difficulty to get the trophy, just beating the last chapter on this setting will not unlock it.
'Not a Cairn in the World' Trophy Guide
To get the 'Not a Cairn in the World' trophy you have to knock over ALL the rock cairns in Madagascar by driving over them. ALL the cairns are in Chapter 10 and at certain points in the mission you will not be able to go back which means you must knock them over in the correct order.
'Relic Finder' Trophy Guide:
There are three 'strange' items you must find to get 'Relic Finder' trophy, these items are a pendant in Chapter 9, a relic in Chapter 12, and a fruit in Chapter 21. These items also count as treasures.
Achievement How to unlock
Buckshot Spread Em
Explosive Rounds Blow Em Up
Gun Upgrade Gun Modder
Holy Assistance Help From Above
Kill The Nazi Ufo Down With Nazi UFOs
Slug Slug It Out
Take It's Head Off Off With Their Heads
Tutorial Complete Now the slaughter can begin