Bestiary entry from the Clan Primer:
This creature always drops a trophy when it is defeated. This trophy is used in the Hunt Club side quest which involves trading in the trophies for items, armor and accessories.
|Common - (55%)||Glimmering Robes|
|Uncommon - (10%)||(Nothing)|
|Rare - (3%)||(Nothing)|
* The Crystal Knight will only appear once you have initiated the Hunt Club side quest. In order to spawn it, you must travel to A Vikaari Kanbhru Ra and completing a circle around to Sthaana Sagittarius before returning to A Vikaari Kanbhru Ra as shown in the picture below:
Use the full map of the Great Crystal if you have trouble finding this spot within the Great Crystal.