On certain levels of the Alien and Marine, you can hear the Predators classic vocal 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 only the Alien can get to.
As the Alien you can eventually get to the jungle and exit in a Marine complex. To the far side is a downed ship with "MARLOW" painted on the side. If you climb up this ship you will find a flat area of land on the other side of the electrified fence. Moving too far however will result in an instant death.
Found in multiple levels are red gas canisters with a small pilot light on them. These can be pushed easily by walking into them. If you can get behind the smart gun, push it as close as you can and strike it once with a heavy attack (should be a tail strike). You will have limited time to flee before it explodes, disabling the smart gun. Note: Some smart guns require nearby terminals to be activated and some simply cannot be turned off, as they are used as a device to herd you in a certain direction.
As the Alien on level 3, the Queen will tell you to get to the bottom of a shaft with a large 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.
ACHIEVEMENT - HOW TO UNLOCK ...That's A Promise - Get Tequila to surgery. Ain't Got Time to Bleed - Heal or regenerate 30 blocks of health in Survivor. Alien vs Predator - Create a new species. Breaking and Entering - Find a way into the Research Lab. Breaking Quarantine - Escape from the Research Lab. Club hopper - Survive The 'Party' at The Club. Come to Mama - Liberate the Matriarch. Elite Sniper - Kill 10 enemies with head shots from the scoped rifle. Exit Strategy - Escape from C-Block. Extinction Agenda - Destroy the Abomination. Eyes of The Demon - Retrieve the ancient mask. Fallen Comrade - Find the Youngbloods in the Jungle. Fortune and Glory - Find all 45 Predator trophy belts. Game Over, Man! - Complete all three Campaigns. Get to The Chopper! - Recover Weyland's datapad. Grim Reaper - Harvest all available civilians in the Alien Campaign. Grunt Hunt - Wipe out all of the Marines in the Colony. Gunslinger - Kill 30 enemies with the pistol. Harsh Language - Discover all 67 Audio Diaries. I Admire its Purity - Complete Alien Campaign on Hard difficulty setting. I Like to Keep This Handy - Kill 2 enemies with one shot with the shotgun. I LOVE the Corps! - Complete Marine Campaign on Nightmare difficulty setting. I Will Never Leave You... - Locate Tequila. It Ain't No Man - Complete Predator Campaign on Hard difficulty setting. It Uses The Jungle - Find a way through Gateway. Let's Rock! - Kill 5 enemies with one burst from the smartgun. Magnificent, Isn't It? - Complete Alien Campaign on Nightmare difficulty setting. Matter of Honor - Discover the Elite Predator's fate. Not Bad for A Human - Get all the Aliens vs Predator achievements. One Big Bug - Defeat the Praetorian. One Ugly Mother - Complete Predator Campaign on Nightmare difficulty setting. Persecution Complex - Achieve Persecutor status more than once in any Ranked Match. Quite A Specimen - Destroy all 50 Royal Jelly Containers. Real Nasty Habit - Get 18060 XP in Ranked Matches. Reclaimer - Retrieve the second artifact. Regicide - Defeat the Matriarch. Scatter Shot - As a team, kill 20 enemies in under 60 seconds in a Survivor match.. Serial Killer - Win 10 Ranked Matches in any Deathmatch mode. Spin Doctor - Kill two enemies with one throw of the Battle Disc. Stay Frosty - Complete Marine Campaign on Hard difficulty setting. Stick Around - Kill 20 enemies with the Combi Stick. The Six Pack - Play with six friends in a Ranked Match. The Uninfected - Finish a Ranked Infestation match as the only remaining prey. Under Pressure - Solve the riddle of the Ruins. Very Tough Hombre - Kill 10 enemies in a row without dying in a Ranked Match. Welcome to The Party - Get 6000 XP in Ranked Matches. Welcome to The War - Play and complete your first Ranked Match in standard Deathmatch mode. World of Hurt - Survive trial by combat. You Have My Sympathies - Help Van Zandt.