If a Blood Arcanist takes the Celestial bloodline, could they take the Empyreal Wildblood? Or would it fall outside of the archetype's abilities? They say the Wildblood is a mutation f the normal bloodline
You can't select the Wilblooded bloodlines since those are only available to Sorcerers with the Wildblooded archetype.
I ask because the Bloodline Development Exploit specifically mentions that it specifically cannot be selected from archetype modified bloodlines.
Blood Arcanist says "A blood arcanist selects one bloodline from those available through the sorcerer bloodline class feature." You select Empyreal and wildblooded through that class feature.
wildblood is an archetype so it's changing and is no longer the sorcerer bloodline class feature mentioned in the arcanist section.
If you took a level in Sorc and picked the wildblood archetype, to take the Empyreal bloodline, you could then advance it's development with Bloodline Development arcana.
However the Arcanist Archetype doesn't allow that option.