Getting Myst Crystals
The easiest way to get Myst Crystal, Myst Fragment, and Myst Cluster early on in Snacko is in the mines.
You will have to finish Restoring the Grassy Plains Obelisk.
Once the Miasma has gone away in the plains, you can go to the mines from the plains by the farm tiles.
When inside, use your pickaxe to hit the golden blocks to get Myst Fragments, Crystals, or Clusters.
Or, kill orange slimes using your Solstice Staff or Sword.
Once you have unlocked Remnant Loom recipes that allow you to put in fragments and clusters to create crystals, you can obtain more Myst Crystals that way.