Here is the full list of all 21 E.T. Armies achievements.
Escape the mothership on time before it blowup
Place bomb on all energy pillars and clear the area
Finish the game on Normal level
Kill all spaceships on roof and make your way to your allies
Under command of FARHAD clear your path and enter the center tower
Survive till the HQ sends you a train to reach the Center tower
Headshot 200 enemies in the game
Destroy all the flying drones on the broken train
Work with Ashkan to escape enemies in wagon railway
Destroy the enemy defense around energy square
Help Ashkan and escape the swarm of enemies
Destroy the last energy source
Survive the Desert and escape with your teammates
Finish the game on Easy Level
Finish the game on Brutal level
Finish the game on Brutal level without dying
Only use Parsis weapons to finish the game
Kill 5 enemies with an explosion
Kill at least half of enemies with pistol!
Kill all enemies on The roof with Gatling turrets
NEVER miss a shot and finish the game