I have a thing in my fan fiction called a spirit Pokemon within my oc Takengrin Endmmar and that is Giratina (aka IMO the best Dragon type Pokemon in the entire franchise).
Other of my versions of characters I have redesgined like for example the elements of insanity, my very first OC named Kamodo the Komodo Dragon, and my OC’s cartoon wifes all have a spirit Pokemon and are able to change into their spirit Pokemon if necessary.
Takengrin Endmmar’s however, specifically changes/evloves into these during the course of the fan fiction/show:
Ultra
Omega
Titan Blood
Spirit Bond
Primal
Spirit Primal