Godaris

Godaris is the most infamous immortal, due to his opposition to closing the Upper Realm. He is of an immortal breed called Beasts, but are colloquially called demons for their more selfish customs and actions (as a culture, individuals can be kind and selfless, but those are not characteristics valued in their culture). Their animalistic appearances are the foundation of their racial name and do not help the evil connotations of their kind.
Beasts come in many forms, more diverse than most other groups of immortals, such as wolf-people (birthing legends of werewolves in the Upper Realm), horse-people (similar in appearance to centaurs), cow-people (leading to stories like the minotaur), and other animal-human hybrids. These immortals have less magical manipulation than many other immortals, but they are made of magic more directly than others. For the same reasons that the Upper Realm is so dangerous (being made from magic and therefore highly susceptible), beasts are the same, except that their anatomical traits give them magical abilities. They are more confined in their magic usage and have more weaknesses than non-Beasts, but their abilities are difficult to recreate by magic alone.
Godaris was a particularly nasty breed of lizard-man, able to regrow limbs (and sometimes even clones) and a lover of high temperatures. It is said he would set himself on fire at times, for leisure (or intimidation). He, among many other Beasts, found themselves capable of more magic beyond their anatomical abilities on the Upper Realm, bringing them to similar capabilities of the other immortals on the Lower Realms. It cost them a lot more to cast, but most liked the power and saw the costs worth it. Godaris most of all.
Just before Regna the Fey closed the Upper Realm, Godaris knew he was about to loose. His and the magic of the other Beasts was simply not enough, nor were their numbers even with mortals under their control. In the final moments before the realms were sealed off, Godaris dove beneath a blade and was split in half across the middle. He regrew his legs and was whisked back to the Lower Realms with the other rebels, but what the others failed to realize in the commotion was that his severed legs had also grown a replacement body. It was only a shadow of himself, but it skittered into the forest and escaped the retrieval.
A mind cannot be fully regrown, and without it, it cannot be fully sustained. It acts as a parasite, latching onto others, typically mortals with little magic, and feeds on their life energy to survive. If he finds a particularly strong host, he uses it to search for a way to reopen the seal between realms, or at least find a way to slip his true self back in.