Red Faction: Guerrilla

All the 16 hidden challenges in RFG to get the description unlocked you must finish half of the required challenge. They can be unlock by doing a regular matchmaking or a custom match. LAN games don't count because they don't give you XP. There are 16 total Hidden Challenges in Multiplayer for you to unlock, here you can see how to unlock each of these challenges. Six of these must be achieved in one life, while the others are overall.P.S Sorry I had to re-post it from the Xbox cheats list so give credit to Shuriken243

Select "Options" at the main menu, then select "Extras". Select the "Enter Code" option, then enter one of the following case-sensitive codes to activate the corresponding cheat function. Enabling codes will prevent the game from being saved.

Gamestop Wrecking Crew maps
Enter MAPMAYHEM as a code.

Gold Hammer
Enter HARDHITTER as a code.

Complete the indicated tasks to unlock the corresponding cheat option. To enable a code, pause game play, select the "Cheats" option, and turn it on.

Cool Turrets
Blow up 100 small hydrogen tanks. When this cheat is active, turrets do not overheat.

Free Upgrades
Complete 50 Guerrilla Actions. When this cheat is active, there is no more salvage charge at the safe house.

Max Morale
Liberate Oasis Sector. When this cheat is active, there is full morale in all sectors all the time.

Max Technology
Liberate Mars. When this cheat is active, EDF/Guerilla/Marauder always has the best armor and weapons.

No Green Alert
Complete 25 killing sprees during the Campaign. When this cheat is active, there are constant EDF assaults.

Super Debris
Destroy 50 EDF owned buildings. When this cheat is active, all explosive impulses and damage from collisions are tripled.

Super Hammer
Kill 100 EDF with a hammer. When this cheat is active, your sledgehammer is extra strong.

Super Jetpack
Destroy 250 EDF supply crates. When this cheat is active, the jetpack recharges at twice the maximum recharge.

Super Sprinting
Mine all ore locations. When this cheat is active, the player can sprint at 1.5x normal speed.

Super Toughness
Locate all missing radio tags. When this cheat is active, it greatly increases the amount of damage you can take, making you harder to kill.

Unlimited Ammo
Destroy 50 EDF flyers. When this cheat is active, you will have unlimited ammunition for all weapons.

Exit a vehicle after it overturns. When it is on its roof, walk near it and re-enter it. Repeatedly tap [Enter Vehicle] and the vehicle will turn over with its wheels back on the ground.

When your health is low during any mission, enter any vehicle for a few seconds. Once you get out of the vehicle, your health/shield will be completely healed. This works anytime, and you cannot die while getting into a vehicle.

Use the following trick to easily unlock the "Super Hammer" cheat, which requires 100 EDF kills with the sledgehammer. Go to Dust near the Chemical Depot that is by the Badlands. Kill a few guards, then go back out of the depot. Wait for cars to pass by, then take them from the civilians and guerrillas. Form a wall using these cars with only two openings just big enough for people to fit through. Wait for the EDF to start coming in through the holes. Take out the sledgehammer and hit them with it. If they start trying to bash the car wall, blow up their cars. You can use the sledgehammer, but it will take awhile. Try using the explosives because the kills do not have to be all in a row. Keep doing this until you have killed enough EDF. Note: Do not go into the Chemical Depot.

Complete the indicated task to unlock the corresponding equipment.

Grinder: Have 12 Guerrilla Actions.
Jetpack: Liberate Oasis sector.
Level 1 armor and Rocket Launcher: Liberate Parker sector.
Level 2 armor: Liberate Badlands sector.
Nano Forge and Guerrilla Express: Liberate Dust sector.
Ore Additive: Have 2 Guerrilla Actions.
Personnel Detector: Have 8 Guerrilla Actions.
Proximity Mines: Have 5 Guerrilla Actions.
Quantum Multiplier: Have 18 Guerrilla Actions.
Shattersmasher Sledgehammer: Have 35 Guerrilla Actions.
Stonebreaker Sledgehammer: Have 25 Guerrilla Actions.
Thermobaric Rocket: Liberate Free Fire Zone sector.

Earn the indicated amount of experience points to unlock the corresponding bonus.

Playlist for Team objective: 50
Alec Mason Character: 100
Badge Group - Guerrilla: 200
Playlist for Siege: 250
Rank 1 Badge: 400
Blair Character: 475
Large Mixer Playlist: 625
EDF Trooper Character: 800
Rank 2 Badge: 1,000
Dan Mason Character: 1,100
Color Group - Aqua: 1,300
Celia Character: 1,400
Badge Group - Weapons 1: 1,700
Pierce Character: 1,900
Rank 3 Badge: 2,000
Sledgehammer - Stonebreaker: 2,450
Color Group - Green: 2,750
Kat Character: 2,900
Jackson Character: 3,350
Rank 4 Badge: 3,500
Badge group - Symbols: 3,800
Sledgehammer - Shattermaster: 3,950
Clark Character: 4,250
EDF Specialist Character: 4,700
Badge Group - Stars: 4,850
Color Group - Crimson: 5,200
Olga Character: 5,600
Rank 5 Badge: 6,000
Sledgehammer - Facecrusher: 6,200
Chuck Character: 6,400
Badge Group - EDF: 6,800
Selma Character: 7,400
Sledgehammer - Bronze Crusher: 7,600
Ian Character: 8,000
Red Color Group: 8,500
EDF Elite Character: 9,000
Sledgehammer - Silver Master: 9,250
Badge Group - Weapons 2: 9,750
Rank 6 Badge: 10,000
Color Group - Orange: 10,300
Kayla Character: 11,200
Sledgehammer - Gold Breaker: 11,800
Kepler Character: 12,600
Badge Group - Backpacks: 13,400
Rachel Character: 13,800
Sledgehammer - Titanium Hammer: 14,600
Rank 7 Badge: 15,000
Ravager Character: 16,000
Color Group - Tan: 17,000
Numah Character: 18,000
Sledgehammer - Skull Digger: 19,500
Krystal Character: 21,000
Sledgehammer - War Hammer: 21,750
Color group - Yellow (yellow): 23,250
Rank 8 Badge: 25,000
Old Coot Character: 26,000
Sledgehammer - Battle Axe: 28,000
Badge Group - Volition: 30,000
Sledgehammer - Bloody Bat: 32,000
Scavenger Character: 34,000
Badge Group - Summoner: 36,000
Rank 9 Badge: 40,000
Color Group - Purple: 42,000
Sledgehammer - Stun Baton: 46,000
EDF Heavy Character: 50,000
Color Group - Rainbow: 54,000
Badge Group - Alter Echo: 58,000
Sledgehammer - Plastic: 60,000
RF Commander Character: 65,000
Badge Group - Marauder: 70,000
Rank 10 badge: 75,000
Color Group - Silver: 85,000
Raider Character: 100,000
Sledgehammer - Ostrich: 120,000
Rank 11 Badge: 150,000

From Main Menu Select Options, Select Extras, Select Enter Code, Enter Code in all Caps.

To repair any vehicle quickly, just use Guerrilla Express while inside your vehicle. The vehicle can now be found in or near the camp you traveled to, with no damage.

Exit a vehicle near the end of a mission. Complete the mission and return to the vehicle. It will be fully repaired.

If you hijack an EDF tank, you are unable to heal it by teleporting to a safehouse. In fact, the tank disappears. You are however able to heal tanks or any other vehicles by going to a demolitions master. Leave the area during the event, and you will fail. After the challenge ends, you should have a full health EDF tank where you left it before the challenge.