All Shy Guys (with the minor exception of General Guy) wear robes that can be red, pink, blue, yellow, green, light blue, black, or white. They are all fairly short and all wear masks with holes on them that represent eyes and a mouth. It is unknown what is behind these masks. However, in Shy Guy's trophy celebration movie in Mario Power Tennis, Luigi sees a Shy Guy without his mask on and is shocked at the sight. Also, in Luigi's Mansion, Luigi can use the Poltergust 3000 to pull a mask off a Shy Guy Ghost. These faces are pure blackness with two glowing yellow eyes. It is unknown whether this is what a Shy Guy's face looks like when it is alive, or it is simply a mirage, as they, like the game's other generic ghosts, were imitations created by Vincent Van Gore.
It is also possible that the Shy Guys' so-called "masks" are not masks at all, but rather faces. In Yoshi's Island DS, the sleeping Shy Guy's mask eye holes are closed, supporting this. Also, the Bandit sub-species of Shy Guy have been shown to have the ability to change the expressions on their masks as if they were their actual faces. The picture shown when Bandit wins in Super Mario World 2 Mini-Battles even suggests that he is able to stick out his tongue. Also, Super Mario RPG's Shy Guys' eye holes comically spin when the Shy Guy is confused, much like people's eyes do in cartoon gags; the Shy Guys of Super Mario RPG are also able to blush on their masks. Spear Guys and Dancing Spear Guys are perfectly capable of moving their mouth holes when chanting and singing, as Super Mario World 2: Yoshi's Island shows. Most recently, in Mario Strikers Charged, Shy Guys have been shown to yet again be perfectly able to change the expressions on their masks. However, most information suggests that Shy Guy's mask is indeed a mask, and what he hides behind is surely something very dark and secret.
Some early Super Mario Bros. 2 artwork of Shy Guys, as well as The Super Mario Bros. Super Show!, depicted Shy Guys as wearing strange, Chuckola Fruit-like badges depicting an angry face. It is unknown what this badge represents; it is possible that it is some kind of emblem to the 8 bits. Another Shy Guy-related element seen only in Super Mario Bros. 2. and The Super Mario Bros. Super Show! are also notable for using game artwork of the earliest forms of Shy Guys, making them tall, stout, and human-like; however, the appearance of Shy Guys was later redesigned to their in-game sprite appearance in Super Mario Bros. 2.
In the first few episodes of The Super Mario Bros. Super Show!, Shy Guys were depicted as being similar in appearance to their game counterparts, though with one large exception - their masks possessed only two holes. They only had eye holes perpetually in a scowling position. Later episodes of the show would have Shy Guys resembling their game versions more with three holes in their mask, all of which were perfectly circular.