In Mythology, Fenrir is depicted as literally a giant Wolf. He has black or red eyes to reflect his dark soul and that he is in league with Loki. The Mythological depiction is a metaphor for reputation, symbolism, and/or what he is known for.
Features to include when drawing:
A Giant Wolf
He is one of Loki's sons
Colors: Black, red - Splash Color = Red
Fenrir represents one of the destructions
In Tradition, Fenrir is depicted as a half-man/half-wolf, akin to a werewolf or the like. He is a beast-man with man thoughts. He has black or red eyes to reflect his dark soul and that he is in league with Loki.
In Tradition, don't depict him as a giant or gigantic, he should be roughly the same size as the Gods. Think larger than life, leader/king of a realm or kingdom.
In Legends, Fenrir is depicted as a military commander with a Wolf symbol, banners, head dress, and the like. He is a Mega-Villain. He should be depicted as a man, not grotesque or ugly, possibly even good looking. He has black eyes to reflect his dark soul and that he is in league with Loki. He is a counterpart to Tyr or Thor in size and strength.