Cythor Fiend

The Cythor Fiends (classisfied as Homindae crystallis by the Imperium) are a race of Xenos with advanced crystal technology and a knack for escaping genocide by the Imperium, native to the Ghoul Stars. They are so powerful the Imperium has basically taken to containing them in their own territory rather than try to outright wipe them out, after they pushed back after an attempted genocide and took back many of their old planets.