The Skullnaga is one of Yn'aga's avatars. After the demon's death at the hands of Sol, Ghaomir’s herald, his body decomposed to the point where only bones remained, preserved by the Nagarot cult as a sacred relic.
After many attempts to bring the Demon back to life, it was thanks to the intervention of the Slathaai, who taught the Animancy discipline to Nargskerak, that the cult was able to bring back a fragment of the demon's life from the dead, sacrificing many souls.
Today, the Skullnaga a mindless monster hungry for souls, but still a powerful and immortal ally.