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