Here's is my OC Eris, but much differently. Originally this is a mixture of Hellhound and Tyranid (wh40k), and maybe I edit all chapters I have of Kingdom Hearts Hellfire to adapt this version. Come on, even she goes with a new species name called as "hellbeast". And if you wonder, her 'exo-shells' are both shells and muscles. And maybe isn't noted by the picture, but she's between toned and muscular with abs.
The reason is that originally Eris groups would have to deal with a Tyranid invasion, and during the fight Eris would lose an arm (but eventually regenerates another) by an hormagant who took as fast as it could to their biomass pool so the queen can try to replicate her, but they're defeated (better said incinerated), queen included, but without warning a mix of Eris and Tyranid borns from the remains. This one behaved wildly and more to her 'succubus' behavior, disobeying the hive mind all the time. Eventually in a future chapter Eris would lose her body, but her heart would be then placed in this body. The reason of changing of ideas is that it could take too long to reach these parts and would forget about them. Besides, I think this form is better for Eris than a pure hellhound.
