Unlock the following skins by reaching the corresponding ranks:
SKIN - RANK
Gibson (Marine) - Rank 2
Claw (Predator) - Rank 3
Warrior Dome (Alien) - Rank 4
Connor (Marine) - Rank 5
Stalker (Predator) - Rank 7
Ridged (Alien) - Rank 10
Moss (Marine) - Rank 13
Hunter (Predator) - Rank 16
Praetorian (Alien) - Rank 19
Johnson (Marine) - Rank 22
Wolf (Predator) - Rank 25
Rookie (Marine) - Rank 28
Spartan (Predator) - Rank 31
Nethead (Alien) - Rank 34
To easily gain XP, search for a ranked match in Multiplayer mode. When it says "One player in game, waiting for more players", quit, and go to the main menu. Then, load a Marine mission on the Normal difficulty with a lot of enemies, such as the Praetorian boss in the "Research Lab" mission. Simply kill enemies now to get easy XP. Repeat as desired.
Avoid Alien Instant Kills:
To avoid being instantly killed by an alien while playing as a Marine in multiplayer, keep your back against the wall.
To make collectibles flash on your HUD when playing as an Alien or Predator, activate FOCUS.
Ventilation shaft as Alien:
As Alien in level 3, the Queen will tell you to get to the bottom of a shaft with a giant fan at the top. As you get near it, another Xenomorph will be swept away and blown into the fan. If you use your Focus, you can see two vents on the opposite wall. select either of them and you can safely jump to it despite the power of the fan. As you go, you will find more vents to hide in. Use them to make your way down.
Out of bounds as Alien:
As the Alien, you can eventually reach the jungle and exit in a Marine complex. To the far side is a downed ship with "MARLOW" painted on the side. Climb up this ship to find a flat area of land on the other side of the electrified fence. Moving too far, however, will result in an instant death.
Disabling smart guns as Alien:
In several levels are red gas canisters with a small pilot light on them. These can be pushed easily by walking into them. Get behind the smart gun and push it as close as possible, then strike it once with a heavy attack (should be a tail strike). You will have a small amount of time to flee before it explodes, disabling the smart gun
In some levels of the Alien and Marine, you can hear the Predator's classic sounds in the background. In some levels as the Alien you can just see the blurry shape of a Predator moving when you enter a new area. There are also Predator Mines laid out in certain areas that can only be reached by Aliens.
In some areas, Civilians will be so frightened of you that they will commit suicide.
ACHIEVEMENT - HOW TO UNLOCK
Not Bad for A Human (50 points) - Earn all achievements.
Game Over, Man! (30 points) - Beat all three Campaigns.
Club hopper (15 points) - Survive The 'Party' at The Club.
Exit Strategy (15 points) - Escape from C-Block.
You Have My Sympathies (15 points) - Help Van Zandt.
Regicide (15 points) - Defeat the Matriarch.
I Will Never Leave You... (15 points) - Locate Tequila.
...That's A Promise (15 points) - Get Tequila to surgery.
One Big Bug (15 points) - Defeat the Praetorian.
Get to The Chopper! (30 points) - Recover Weyland's datapad.
Come to Mama (15 points) - Liberate the Matriarch.
Breaking Quarantine (15 points) - Escape from the Research Lab.
Grunt Hunt (15 points) - Wipe out all of the Marines in the Colony.
Under Pressure (15 points) - Solve the riddle of the Ruins.
Grim Reaper (15 points) - Harvest all available civilians in the Alien Campaign.
Alien vs Predator (30 points) - Create a new species.
It Uses The Jungle (15 points) - Find a way through Gateway.
Fallen Comrade (15 points) - Find the Youngbloods in the Jungle.
Matter of Honor (15 points) - Discover the Elite Predator's fate.
Eyes of The Demon (15 points) - Retrieve the ancient mask.
World of Hurt (15 points) - Survive trial by combat.
Breaking and Entering (15 points) - Find a way into the Research Lab.
Reclaimer (15 points) - Retrieve the second artifact.
Extinction Agenda (30 points) - Destroy the Abomination.
Stay Frosty (15 points) -Beat Marine Campaign on Hard difficulty setting.
I Admire its Purity (15 points) -Beat Alien Campaign on Hard difficulty setting.
It Ain't No Man (15 points) -Beat Predator Campaign on Hard difficulty setting.
I LOVE the Corps! (30 points) -Beat Marine Campaign on Nightmare difficulty setting.
Magnificent, Isn't It? (30 points) -Beat Alien Campaign on Nightmare difficulty setting.
One Ugly Mother (30 points) -Beat Predator Campaign on Nightmare difficulty setting.
Harsh Language (15 points) - Discover all 67 Audio Diaries.
Quite A Specimen (15 points) - Destroy all 50 Royal Jelly Containers.
Fortune and Glory (15 points) - Find all 45 Predator trophy belts.
Scatter Shot (15 points) - As a team, kill 20 enemies in under 60 seconds in a Survivor match..
I Like to Keep This Handy (15 points) - Kill 2 enemies with one shot with the shotgun.
Spin Doctor (15 points) - Kill two enemies with one throw of the Battle Disc.
Let's Rock! (15 points) - Kill 5 enemies with one burst from the smartgun.
Elite Sniper (15 points) - Kill 10 enemies with head shots from the scoped rifle.
Stick Around (15 points) - Kill 20 enemies with the Combi Stick.
Gunslinger (30 points) - Kill 30 enemies with the pistol.
Welcome to The War (15 points) - Play and complete your first Ranked Match in standard Deathmatch mode.
Killer Instinct (15 points) - Win your first Ranked Match in standard Deathmatch mode.
Serial Killer (30 points) - Win 10 Ranked Matches in any Deathmatch mode.
Very Tough Hombre (15 points) - Kill 10 enemies in a row without dying in a Ranked Match.
Persecution Complex (15 points) - Achieve Persecutor status more than once in any Ranked Match.
The Six Pack (30 points) - Play with six friends in a Ranked Match.
Ain't Got Time to Bleed (15 points) - Heal or regenerate 30 blocks of health in Survivor.
The Uninfected (30 points) - Finish a Ranked Infestation match as the only remaining prey.
Welcome to The Party (30 points) - Get 6000 XP in Ranked Matches.
Real Nasty Habit (50 points) - Get 18060 XP in Ranked Matches.