This will be your last achievement you'll get in the title update (unless if you haven't failed a level already).
Already by completing level 1 (and completing level two like I did) you should have 12 crystals and these achievements:
Now, to get last crystal hunter achievement, all we need to do is finish level three, which contains 8 crystals. I first moved the box to the left of the mushroom guy all the way to the left and collected the two crystals along the way. I then got the two crystals on the top left by crossing the bottom portion of the partial bridge first then got back on the top portion. you could now either use the three remaining boxes to create a bridge across, or move them out of the way to cross the other partial bridge. Once those four crystals have been collected, we'll now have 20 collected total throughout the first three levels.