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

Unlockables

1 Life: 10 Kills - 1 Weapon Kill 10 people with the same weapon in one life.
1 Life: 15 Bonuses Get 15 different bonuses in one life.
1 Life: 25 Bonus XP Gain 25 bonus XP in one life.
1 Life: 5 XP - 5 Backpacks Get 5 XP with 5 different backpacks in one life.
1 Life: 50 XP Gain 50 core or bonus XP in one life.
1 Life: Kill - 5 Weapons Kill 5 people with 5 different weapons in one life.
10 Kills - Every Weapon Kill ten players with each individual weapon.
10 Wins - Every Game Type Win 10 matches in every gametype.
100 Wins Win 100 matches. (Mode does not matter)
100 XP - Every Backpack Gain 100 XP with each individual backpack.
100 XP - Every Weapon Gain 100 XP with each individual weapon.
1000 Kills - 1 Weapon Kill 1000 players with one weapon.
5 XP - Every Bonus Event Gain 5 XP with each bonus event.
500 XP - 1 Bonus Event Gain 500 XP with one bonus event. (Ex. Assist)
5000 XP - 1 Backpack Gain 5000 XP with one backpack. (Ex. Rhino)
5000 XP - 1 Weapon Gain 5000 XP with one weapon. (Ex. Assault Rifle)

Demons of the Badlands DLC Trophies - Complete each requirement to get the specified Trophy. There are 7 Bronze Trophies and 3 Silver Trophies.

Unlockables

A Greater Purpose (Silver) Complete Redemption.
Ares’ Bloodlust (Bronze) Destroy the 4 Marauder War Totems.
Bound in Blood (Bronze) Complete Rescue.
Deliverance Defender (Silver) Complete Marauder Actions.
Family Vengeance (Silver) Complete Retribution.
Mobile Bombs (Bronze) Destroy 100 EDF vehicles.
Purge the Valley (Bronze) Break the EDF Control of the Mariner Valley.
Structural Integrity (Bronze) Destroy all Medium and High Priority Targets in Mariner Valley.
The Power of One (Bronze) Collect 75 Marauder Power Cells.
Tumbling Down (Bronze) Beat all Pro times in Mariner Valley Demo Masters and Transporters.

Insane Difficulty - Complete the campaign to unlock Insane mode.

Trophies - Complete each requirement to get the specified Trophy. There are 42 Bronze Trophies, 5 Silver Trophies, 3 Gold Trophies, and 1 Platinum Trophy.

Unlockables

A Winner is You! (Bronze) Win 250 matchmaking games.
Battle Scarred (Bronze) Earn 10,000 XP in Multiplayer.
Best Friends Forever (Silver) Kill 100 EDF with the sledgehammer during the Campaign.
Broken Supply Line (Bronze) Destroy 250 EDF supply crates.
Can’t Get Enough (Bronze) Play every mode on all maps in Wrecking Crew.
Check Your Map (Bronze) Finish a match on every map in Multiplayer.
Clean and Righteous! (Bronze) Destroy 5 High Importance targets.
Coming Down! (Bronze) Destroy 50 EDF owned buildings.
Coup D’etat (Bronze) Liberate Eos Sector.
Courier of Pain (Bronze) Score 5,000 kills in Multiplayer.
Death From Above (Bronze) Liberate Dust Sector.
Detective (Bronze) Complete 8 hidden challenges in Multiplayer.
Disaster Area (Silver) Destroy 1 billion credits worth of EDF property.
Doing Your Part (Bronze) Kill 10 enemies in a Matchmaking Match.
Don’t Tread On Me (Bronze) Liberate Oasis Sector.
Doozer (Bronze) Reconstruct a Damage Control target.
Experimenter (Bronze) Complete 4 hidden challenges in Multiplayer.
Field Tested (Bronze) Earn 1,000 XP in Multiplayer.
Free Your Mind (Bronze) Destroy all instances of propaganda.
Freed Space (Bronze) Destroy 50 EDF flyers.
Freedom Fighter (Bronze) Complete 50 Guerrilla Actions.
Friendly Skies (Bronze) Liberate Badlands Sector.
Got Any Fingers Left? (Bronze) Beat all Pro times in Demolitions Master.
Grab Some Popcorn (Bronze) Enter Spectator mode and enjoy the show!
Guerrilla (Bronze) Complete 25 Guerrilla Actions.
Insurgent (Bronze) Complete 5 Guerrilla Actions.
Jack of all Trades (Bronze) Score 10 kills while wearing each backpack.
Juggernaut (Bronze) Destroy a Siege target.
Just the Beginning (Bronze) Win a Matchmaking match.
Lost Memories (Bronze) Locate all missing radio tags.
Mad Genius (Silver) Complete 16 hidden challenges in Multiplayer.
Martian Tea Party (Silver) Complete 2 missions for the Red Faction.
One Man Army (Bronze) Complete 25 killing sprees during the Campaign.
Party Time (Bronze) Play all Wrecking Crew modes once.
Power to the People (Bronze) Raise the Morale of 3 sectors to 100%.
Red Dawn (Gold) Liberate Mars.
Red Faction Member (Gold) Play online with another player who has completed the Campaign.
Red Faction: Guerrilla (Platinum) Unlock all Trophies in Red Faction: Guerrilla
Revolutionary (Silver) Complete all Guerrilla Actions.
Spread the Word (Bronze) Liberate Parker Sector.
Start of Something Special (Bronze) Play 5 Matchmaking matches.
Tank Buster (Bronze) Blow up 100 small hydrogen tanks.
The High and Mighty (Bronze) Kill a flying opponent using a remote charge stuck to them.
Tools of the Trade (Bronze) Score a kill with every weapon in Multiplayer.
Topher Would Be Proud (Bronze) Play 250 matchmaking games.
Try Anything Once (Bronze) Finish a match in every mode.
War Veteran (Gold) Earn 100,000 XP in Multiplayer.
Warp Speed (Bronze) Beat all Transporter Pro times.
Welcoming Committee (Bronze) Complete the Tutorial mission.
Working the Land (Bronze) Mine all ore locations.
Wrecking Ball (Bronze) Score 25 million points worth of destruction in Wrecking Crew.

Unlock each cheat by completing its requirements. After a cheat is unlocked, it can be turned on at any time by pausing the game and going to Options>Cheats.

Cool Turrets (Turrets Don't Overheat) Get the Tank Buster trophy (Blow up 100 small hydrogen canisters)
Max Morale (Max Morale in all Sectors) Get the Don't Tread on Me trophy ( Liberate Oasis Sector)
Max Technology (EDF, Guerillas, and Marauders receive superior weapons and armor) Get the Red Dawn trophy (Liberate Mars)
No Green Alert (Alert Status Never at Green) Get the One Man Army trophy (Get 25 killing sprees during campaign)
Super Debris (Explosion and Collision Damage Greatly Increased) Get the Coming Down! trophy (Destroy 50 EDF owned buildings)
Super Hammer (Increase Hammer Damage) Get the Best Friends Forever trophy (100 kills with the sledgehammer during campaign)
Super Sprinting (Sprint speed increased by 50%) Get the Working The Land trophy (Mine all ore locations)
Super Toughness (Increased Physical Resistance) Get the Clean and Righteous! trophy (Destroy 5 High Importance Targets)
Unlimited Ammo (Unlimited ammo for all weapons) Get the Freed Space trophy (Destroy 50 EDF flyers)