Fafnir Mitchell is the son of Daniel Mitchell and Corrin and the twin brother of Saphira Mitchell. He's the only member of the family that does not possess a Klyntar symbiote, but to make up for it, he possesses a powerful artifact that gives him extreme power, at a cost.
Fafnir's behavior shifts depending on the situation: he's friendly, if a bit strange, when just dealing with family and friends; neutral, while still a bit strange, when around strangers; and ruthlessly vicious, as well as strange to the extent of being 'creepy' when in a fight.
In major battles, the Death Stone Energy he's absorbed makes him turn utterly and completely callous and ruthless, willing to carelessly slaughter any opponent who crosses him. Many are the times he's performed an action he's regretted in this mode. That said, he revealed he DID like the appearance of the spirit that possesses him during this time, so he created combat gear that resembles it.
As the son of Daniel Mitchell and Corrin, Fafnir possesses the ability to transform into some form of hybrid between a First Dragon and a Manakete Divine Dragon. Furthermore, he also possesses Psionic Powers from his father's Avatar and Ethereal DNA.
Fafnir, on one of his journeys, discovered a powerful artifact known as the Death Stone, a relic that imbues the user with extreme levels of power, but causes them to be partially possessed by the spirit of Death, warping the individuals personality into a perversion of the user's. As such, Fafnir only utilizes the stone in major battle.
It's unknown if this is due to his extreme level of training or his connection to the Death Stone, but Fafnir also possesses a great deal of martial prowess, be it on the field of battle or serving as a tactician.