Here is the full list of all 37 Alien Robot Monsters achievements.
Gain 20 stars
Build 200 towers
Destroy 99 robots with satellites
Destroy 100 robots with snipers
Fire 256 sniper rounds
Field 256 marines
Defeat Forest biome boss
Use 1337 hand grenades or mortar rounds
Destroy a robot with native arrows
Build 50 towers
Stun 384 robots
Destroy 100 robots in melee
Gain 10 stars
Field 64 marines
Destroy 50 robots in melee
Field some space marines
Start your colonization of Planet X
Defeat Wasteland biome boss
Defeat Swamp biome boss
Defeat Mountain biome boss
Defeat final boss
Complete all Planet X levels
Save the natives
Fire 500 missiles from orbit
Deploy 32 reinforcements
Deploy 128 reinforcements
Build 400 towers
Build 800 towers
Gain 30 stars
Gain 40 stars
Gain 50 stars
Gain 75 stars
Gain 90 stars
Gain all 111 stars
Destroy 128 robots with fire
Destroy 128 robots with Atomizer
Instakill 50 robots