Here's the reference for Runt's humanoid form. His design is very strange to me but still enjoyable at the same time.
He takes this form whenever people or humans would seemingly be more scared of him as a wolf. He doesn't remove his wolf features, however. Instead, you are greeted by the abnormally tall, wraith thin, mix between what would make a man and a beast. A form that exists only with the intention to mock the idea that looking "more human" would be less scary.
Fun little fact that's semi-related: Depending on their upbringing and personality, a nightmare wolf's appearance leans towards a specific trait that will then be exaggerated. Runt's status as the "runt" of the litter is the reason he takes the forms of something emaciated whenever he shapeshifts. Compared to his siblings, he is the smallest and the weakest, and thus ate the least.