Folklore
The Devil is considered a pure spirit with no corporeal substance meaning it is impossible for us humans to create an accurate image of him. They can change their appearance to appeal to the human asthetic though, the same as angels do. It is said though that the devils appearance and essence are uglier and more horrific than humans can even imagine. This can be backed up by the thought that any one or thing that distances themselves from God, who is to be the most beautiful and perfect being in existance, the Devil is on the other end of the spectrum.
The Devil does have the ability to change its appearance is the important point. An example of this is with St. Pio of Pietrelcina. While the Saint was alone the devil has appeared to him multiple times as a dog, Jesus, Mother Mary, a confessor, the Father Guardian of the Convent he resided in, as well as a beautiful naked woman.
He can appear to people in different forms (even as inanimate). Similar to demons, there can be a scent related to presence. These often appear during a cleansing and can appear in the scent of sulfur, animal and human excrement, and other foul scents. It can also appear as small noises like rustling along with tactile sensations like wind blowing.
Amorth, G., Stimamiglio, S., & Fasi, C. J. (2016). An exorcist explains the demonic: The antics of satan and his army of fallen angels. Sophia Institute Press.