To obtain a Crystal Prism, you need to find and kill Mirror Maidens over Level 40+. Upon eliminating these Fatui enemies, they have a chance to drop Crystal Prism. Anything above Lvl 40+ also has a chance to drop Dismal Prism.
To get Mirror Maiden to become Lvl 40+, you need your World Level to become World Level 2 or higher. The most efficient WL to farm anything that needs Lvl 40+ is WL 4, as enemies are between Level 42 and 62. This will give you the most consistent enemy Lvl past 40+. Anything below you will find them, but not as often.
To get to WL 4, you need to have completed the following.
- Be on World Level 3
- Be Adventure Rank 35
- Clear Ascension Quest 2
Mirror Maidens are spread out all over Inazuma. The fastest way to get around is to use the Waypoints, and travel around each island and then move on. The images below are where you can find Mirror Maidens in Inazuma.
- Type: Common Ascension Material
x3 Dismal Prism + 25 Mora = x1 Crystal Prism