Here is the full list of all 41 ALIENS INVADED OUR PLANET achievements.
Play as Cowboy 04
Play as Cowboy 02
Play as Prisoner
Play as Santa
Use Potion Automat
Play as Crusader
Pick 50 PowerUp
Jump 250 Times
Defeat Blind Slime
Shoot 500 Bullets
Play Until The 10th Day
Defeat Mr. One Eye
Kill 100 Alien
Use Weapon Automat
Play as Skeleton
Kill at least one Alien
Defeat First Boss
Defeat Third Eye
Defeat Piece Of Garbage
Defeat Petrol Man
Defeat Mech Brain
Defeat Invisible Hand
Defeat Flying Thing
Defeat Psychopath
Throw 50 Dynamite
Drink 25 Health Potion
Drink 25 Armor Potion
Spend 100K Points
Use Magic Ball
Make x50 Combo
End The Day Under 25 HP
Play Until The 20th Day
Play Until The 30th Day
Play Until The 40th Day
Play Until The 49th Day
Play as Cowboy 01
Play as Cowboy 03
Play as Cowgirl
Unlock and Carry All Weapons
Complete 5 day in Impossible Difficulty
Help a Friend Up