Aliens: Colonial Marines

You must kill 2 Xenomorph enemies, the human enemies does not count. Easiest way to get this achievement is to kill 2 Xenomorphs with the underslung grenade launcher from the pulse rifle.

You get challanges as you play the game, complete anyone of them to unlock.

Unlocks when you've finished the first mission

Towards the end of mission 9 (Hope in Hadley's) there is a fight with a crusher. Once it appears, find high ground to avoid damage from it. Kill using your explosives and shooting the body. You must get the kill for this to count. Use restart checkpoint to your advantage if you're damaged by it or don't get the kill. Can also be done in a multiplayer game.

Unlocks when you've finished mission 3 (Sulaco Falls).

When a Xenomorph grabs your partner, simply free him from the alien's attack.

Kill a Xenomorph thats attached to the walls or ceiling.

Revive your co-op partner in a co-op match to unlock.

Unlocks when you've finished mission 11 (Home).

Early in mission 2, keep an eye on the walls to find a keypad.When you use it, it will unlock a door you recently passed that was locked. Once you enter this room, the achievement will unlock.

Stand against a Xenomorph and kill it with a shotgun.

Kill 10 Xenomorphs that are coming out of vents on the roofs or walls.

The earliest you can unlock this achievement is when you reach level 18 for your marine. Upgrading the combat pistol is probably is the easiest weapon to get this with. It has 3 upgrades needed for the achievement. A weapon skin is also needed.

Experience is earned from kills, collectables, completing challenges, match bonuses and campaign chapters completed.

Simply reach rank 2 as a Marine to unlock.

Complete the end of mission 3 (Sulaco Falls) under 2:30 minutes to unlock.

Complete the game from start to finish.

Defeat the Raven in under 1:10 minutes on Soldier difficulty or higher. If you're struggling, pause and select "restart checkpoint" to try again

The earliest you can unlock this achievement is when you reach level 18 for your marine. Upgrading the combat pistol is probably is the easiest weapon to get this with. It has 3 upgrades needed for the achievement

Have another player join your game.

These look like small laptop computers and highlighted in a light blue color when you're close. Collect all 12 to unlock.

Collect all 6 legendary weapons in the game. These are:

Level 1- Hick's Shotgun
Level 4- Gorman's Pistol
Level 5- Hudson's Pulse Rifle
Level 6- Vasquez's Smart Gun
Level 9- Vasquez's Pistol
Level 10- Frost's Flamethrower

The Firebomb is unlocked at rank 4. Kill 3 alien enemies with a single bomb to unlock. Human enemies does not count for this achievement.

Unlocks when you complete mission 9 (Hope in Hadley's).

Experience is earned from kills, collectables, completing challenges, match bonuses and campaign chapters completed.

Simply reach rank 20 as a Marine to unlock.

The M56A2 Smart Gun can be found in Mission 4, simply get 10 kills with it to unlock. You can restart the checkpoint if needed.

When a Facehugger jumps at you you wil grab onto it, simply throw it away from your face to unlock.

Commendations are the points you receive to purchase upgrades with. These are earned each time you rank up.

Simply track 100 targets on your Motion Tracker to unlock.

Newt's doll can be found in mission 5 (The Raven)

Set up a UA 571-C Remote Sentry - part of the story.

Complete mission 7 without anybody setting off any alarms.The very first scientist will spot you and set off an alarm. This is inevitable, but won't influence the achievement.

Melee attack a Lurker alien that's jumping towards you. Works in single player and multiplayer.

This achievement unlocks when you finish the campaign on Veteran difficulty

Look out for the dog tag collectables as you play the game, collect one for this achievement.

Collect a legendary weapon to unlock this achievement.

Unlocks when you've finished mission 5 (The Raven).

Simply change your Marine loadout found at "versus", "edit loadouts", "marine loadouts" for this achievement.

Collect all 35 dog tags found in the game. One of the dog tags was glitched and had to restart from checkpoint to unlock but this achievement is unlockable.

Best done in 1vs1 match with a friend, or the spitter aliens can be found in mission 6. Simply use a long range gun to kill them without being hit. If you are hit, restart from checkpoint.

Complete all Campaign levels on Ultimate Badass difficulty.

Unlocks when you complete mission 8 (Rampart).

Simply change your Xenomorph loadout found at "versus", "edit loadouts", "Xeno loadouts" for this achievement.