Item Duplication (Cooperative Mode)
You can perform this cheat anywhere in the game, but it works best if you put it to use near a checkpoint and bench. You'll need to be playing with a friend, preferably one who is equipped with a headset so that you can communicate as needed. Start by giving your friend the items you wish to duplicate. After the trade is completed, exit out to the main menu and then immediately have the friend who received your loot save and quit from the pause menu. The trick only works if you follow that precise order, and quickly. If you did it properly, both players should now have the desired items in their inventory.
When picking up an artifact, advance to the next location to go past a doorway. Once you have passed the door, let it shut and reopen. Now return to the location where you found the artifact and in its place you should find resources such as the semiconductors, tungsten, scrap metal, transoucer and health packs. You can repeat this trick as often as you like.
Log Collection Unlocks
You'll gain access to additional gear by collecting the various logs in Dead Space 3.
MK-II Overclocked Module Set - Collecting all Logs
Research Circuit Set - Collect all Text Logs
Comms Circuit Set - Collect all Audio Logs
Artifact Collection Unlocks
You can gain access to additional items for your Artifact Collection by finding artifacts, as indicated below.
MK-II Overclocked Tip Set - Collect all Artifacts
Flight Suit - Collect all Artifacts
EarthGov Circuit Set - Collect all EarthGov Artifacts
Unitologist Circuit Set - Collect all Unitology Artifacts
S.C.A.F. Circuit Set - Collect all S.C.A.F. Artifacts
Alien Circuit Set - Collecting all Alien Artifacts
Optional Mission Unlocks
You can receive special rewards for completing optional missions, as noted below.
MK-II Overclocked Frame Set - Complete all optional (including co-op) missions
Hostile Environment Suit - Complete all optional (including co-op) missions
Weapon Collection Unlocks
You can gain access to additional goodies by satisfying the corresponding conditions.
Crafter's Circuit Set - Collect all weapon parts
Deep Dig Suit - Collect all weapon parts
Builder's Circuit Set - Collect all blueprints
MK-II Overclocked Attachment Set - Collecting all circuits
Completing the New Game+ mode on the "Classic" setting will unlock devil's horns.
Complete the game on various difficulty settings to gain access to additional modes and content.
New Game+ - Completing the game once on any difficulty
Retro Mode - Completing the game in Hardcore Mode
Dead Space Legends Suit Set - Complete the game once
+3 CLP Circuit Set - Complete the game on Casual difficulty
+3 RLD Circuit Set - Complete the game on Normal difficulty
+3 SPD Circuit Set - Complete the game on Hard difficulty
+3 DMG Circuit Set - Complete the game on Impossible difficulty