Here is the full list of all 44 Cubemen achievements.
Kill 50,000 Enemy Cubemen
Collect 50 Heal Bonuses
Collect 150 Bonuses
Collect 50 Freeze Bonuses
Collect 50 Destroy Bonuses
Play & Win all Defense Levels
Kill 10,000 Enemy Cubemen
Buy 900 Cubemen
Collect 100 Bonuses
Collect 20 Heal Bonuses
First time you win an Individual Mayhem game
First time you win a Team Mayhem game
First time you win a Skirmish Game
Earn 90,000 Cubes
Collect 20 Destroy Bonuses
Collect 20 Freeze Bonuses
Collect 50 Bonuses
Buy 500 Cubemen
Kill 5,000 Enemy Cubemen
Earn 50,000 Cubes
Earn 25,000 Cubes
Collect 10 Bonuses
First time you earn a 4x Multiplier
First time you earn a 2x Multiplier
Buy 150 Cubemen
Kill 1,500 Enemy Cubemen
Earn 5x Platinum Medals
First time you earn a 10x Multiplier
First time you earn a 7x Multiplier
First time you earn a 5x Multiplier
Earn 10,000 Cubes
First time you earn a Gold Medal
First time you earn a Bronze Medal
Earn 5,000 Cubes
Buy 50 Cubemen
First time you earn a Platinum Medal
First time you earn a Silver Medal
Kill 250 Enemy Cubemen
Earn 1,500 Cubes
First time you win a Defense Game
Kill 25 Enemy Cubemen
Earn 50 Cubes
Earn 500 Cubes
Earn 150 Cubes