Another achievement that is very easy to unlock.
Level 1 has seven crystals. If you completed the level you should have:
How I proceeded to unlock this one is by completing level 2 in its entirety, which isn't too hard to complete. Push the boxes in front of you and collect the one crystal in the top right, then use the two boxes in front of you to create a bridge across. Once the level is complete, you'll have 12 crystals under your belt.
EDIT: According to the Xbox Achievements forums (and confirmed by Shinnizle), you can simply play level 1 again to unlock this if you already completed the level once. Credit goes to bLaKgRaVy on the Xbox Achievements forums.https://www.xboxachievements.com/forum/topic/484388-mushroom...
This will mean you'll only need to play the level one more time to unlock: