Here is the full list of all 21 Grass Cutter trophies - there are 4 bronze, 8 silver, 8 gold and 1 platinum.
Good job! Completed all tasks!
Face the monsters 50 times
Drive by 10 times on the sand
Disable 50 monsters
Scare the dogs 20 times
Eliminate multiple monsters in less than 1 second
Use a bomb
Eliminate robot
Gather up energy when there is less than 5% left
Eliminate quadcopter
Get wet in the rain
Take a mud bath 20 times
Immerse the first box
Dive into the water 20 times
25 times, purchase 15% of the energy
Cut 1000 squares with grass
Break 100 barriers
Scare the cats 15 times
Make the first purchase
Scare the birds 50 times
Complete the first level