This guide will show you where the crystals but not directly tell you how to get them.
The images are pretty good hints.
Achievements are awarded after you close the game.

Go back to the first island after you've learnt about the Shift ability (second island) to collect the crystal.

Jump toward start from here to collect crystal

Collect the crystal as you are launched by the mushroom


Walk along the Red platform then shift

Fall from above


Raise the platform from below then climb back up

Collect the crystal after being launched by the mushroom

After all the areas are completed, in the hub go to the right and activate the wall switch.
Complete the bonus section for 100% !

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https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2880052179