Whilst not an exact copy of Ghenyfhar, it is a suitable approximation.

Ghenyfhar is a muscular human, though due to various treatments given to himself, he isn't as human as he used to be.
He has grown a pair of vestigial arms, which he uses to aid himself in combat, with his natural arms swinging a lucerne hammer at foes from beyond the reach of most martial combatants, one vestigial limb holding a tower shield, and the other holding potions and other concoctions at the ready.
He has also grown a creature from his own flesh, a tiny creature that resembles a Compsognathus. Yet whether by accident or design, where the familiars to wizards and witches are often timid and in need of protection, Ghenyfhar releases his flesh-beast into battle, where it grows to the size of an adult human, getting stronger in the process.

Ghenyfhar often self-medicates during conflicts, drinking potions or injecting himself with syringes of something known only to him, and when others try, causes them to be sick. Yet somehow it can cause him to grow in size, stretch his limbs further, or somehow even distort reality and cause his very image to blur.

Ghenyfhar is on a crusade against the gods and their worshippers, claiming that they don't deserve to be worshipped, and it is mortals who are powerful. Self belief allows mortals to shape the world around them, and can be so powerful that a naive farmhand would not tell a god apart from the greatest of wizards. So why should we worship them, die in their causes, and fight their wars for them?
His strength of conviction is so strong, it causes those who claim to receive their power from gods to struggle to cast their spells on him, and when they do so, to be less effective than those who accept the preachings and dogma they spout.