Here is the full list of all 18 Forest Guardian achievements.
To reach level 12
To reach level 11
To reach level 10
To reach level 9
To reach level 8
To reach level 7
To reach level 6
To reach level 5
To reach level 4
To reach level 3
To reach level 2
Die 30 times from the plants
Die 20 times from the Frankenstein
Click
Shoot 200 times
Level one is started
Start a new game
Spend on level 10 for more than two minutes