Mordenkainen I pictured as tall, lean, with a pale complexion tanned by sun and weather. His features are sharp, eyes gray. His hair is rather byshy, with a long moustache but no beard. He favors garments of gray with black or bright blue accents--girdle and blouse for example. His age apears to be somewhere around 50.
Bigby I envisioned as of medium height, bald, with prominent nose and large, dark eyes. He is also around age 50, but as he is rather plump, Bigby has few wrinkles. his hands are large and long-fingerd. His clothing is generally of deep green.
That's enough of that
Cheers,
Gary