While playing the game, there will be brown/gray blocks you can smash with either Grouchy, Gutsy or Hefty. They are not found in every level. I didn't use any of these smurfs much in my first playthrough, but I found a way to get the achievement out of the way quickly if you do not feel like waiting on the smurf change move (beat the game to get it) or just want the achievement out of the way.
Play level 4-4. There are 48 blocks in this level and it's very short. I used Gutsy Smurf because his dash move helps get through the level quickly and it's easy to smash the blocks with him.
There are 12 blocks in the first half of the level close to each other. Climb on the lower blocks and smash the top ones first because you need the lower blocks to reach the top ones. The other 36 are in one huge block in the 2nd half of the level. Just dash level to right and break them all. If you play 4-4 twice, that will leave just 4 blocks you need to get the achievement.
Blocks can be found in:
World 1-3 and 5
World 2- 4 and 5,
World 3- 2, 3, 4, and 5
World 4- 1, 2, and 4
World 5- 1, 2, 3, and 4
World 6- 2 and 5