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