The dragon is an earth dragon.
From fighting in the labyrinth and absorbing Veldora's aura the dragon evolved into a dragon king class.
The dragon was granted a name by Ramiris and Rimuru gave them 5000 souls, which allowed it to evolve into a True Dragon King. Upon its evolution, it obtained a humanoid form, which is different from Milim's draganoid form in that Milim is a Spirit Form species, while the Dragons are a corporeal species that have changed forms (they are bound to their bodies). Though it had equal stores of energy to the Ten Lords of the Labyrinth, had lower fighting prowess, and thus decided to train in its new body.
Dragon - 20 meter dragon (assumed).
Dragon King - 20 meter dragon (assumed).
True Dragon King - Beautiful Humanoid form.
Earth Elemental Control.
|Ch||Evolution Stage||Trigger for Evolution||Rank||EP||New Skills/Abilities|
|Adult Dragon||Collected by Milim||A||Battle||Physical attacks with fangs and talons
Elemental attacks - Earth
|146||Dragon King||Veldora Aura and Fighting||A+|
|164||Dragon King||Name by Ramiris
5000 souls by Rimuru