Cheat mode:
Note: This procedure involves editing a game file; create a backup copy of the file 
before proceeding. Use a text editor to edit the "settings.ini" file in the game 
folder. Add one of the following entries to the file followed by "= 1" to enable that 
code or "= 0" to disable it. For example, insert the following line in the file to 
enable gore mode: 

goreOverride = 1

Effect - "settings.ini" entry  
God mode - instagib 
Toggle gore - goreOverride  
Toggle HUD - HUD 
Unknown - smartbomb 
Unknown - weakThrax 
Unknown - audio 
Unknown - music 
Unknown - FMVmusic 
Unknown - showFMV 
Unknown - screenText  
Unknown - fullscreen  

Weapon challenges:
Collect all of the Titan Tablets, Priest's Amulets, and Emperor's Coins. Deposit all 
of them in the appropriate pillar to make a giant stone tablet appear in the middle 
of Elysiam. Activate the tablet to start the weapon challenges.

Annihilation weapon:
Win Axe Challenge 4 in the weapon challenges.

Invictus Gladius weapon:
Win Sword Challenge 4 in the weapon challenges.

Olympus Cleavers:
Win Gauntlet Challenge 4 in the weapon challenges.