Here is the full list of all 17 DEFENDERS OF THE FALLEN ISLAND achievements.
Gain 75 levels
Gain 25 levels
Gain 50 levels
Gain 100 levels
Gain 125 levels
Gain 150 levels
Gain 175 levels
Gain 200 levels
Earn 1.000.000.000 gold
Gather 1.000.000 resource
Kill 100.000 Invaders
Kill 1.000.000 Invaders
Use radar 1.000 times
Build 500 walls
Build 1000 turrets
Take 1.000.000 damage
Kill 100 Titans