Here is the full list of all 12 Gnumz: Masters of Defense achievements.
Use 200 spells
Upgrade any spell to the maximum level
Buy all the upgrades for one of the traps
Destroy 1,000 enemies
Destroy 5,000 enemies
Destroy 10,000 enemies
Complete all levels of any episode with 3 stars
Earn 240 stars
Lose 3 times in a row
Complete a level with only one piece of ore remaining
Only one enemy attacked the base
Complete a level without using spells