Shyguys are enemies in the Super Mario Bros. series of games. Alongside Goombas, Piranha plants and Koopa Troopas, they are the most common enemies in the Mario series.

The Shyguy began as an enemy in a Japanese game titled Doki Doki Panic. This game never made it to the U.S. in its original form, but was transformed into Super Mario Bros. 2. Most of the enemies in the game were from the Japanese version, which included Bob-ombs, Snifits, and Shyguys. These characters are now instantly recognizable as Mario's enemies, even though they were intended for an entirely different environment. Lately, they've taken refuge in such locales as Yoshi's Island and Shy Guy's Toy Box.

Shyguys, as the name suggests, are very shy. They always have masks covering their faces, the only parts not covered are the eyes and mouth. Shyguys can wear different colors, such as red, blue, green, yellow or purple. Their attacks usually consist of simply running into the hero, although some use slingshots. Some varieties, like Snifits and Snufits spit projectiles like the Octorok, while others may catch fire, such as Pyro-guy. They have also come up with some very peculiar inventions over the years, such as walking on stilts, bouncing on pogo-sticks, and piloting submarines. In the Yoshi's Island game, Shyguys could be turned into eggs by Yoshi and it was common for Shyguys to pop out of pipes until Yoshi couldn't make any more eggs.

In Paper Mario (N64), the Shy Guys played an essential role in one of the chapters; the boss (General Guy) at the end of Shy Guy's Toy Box had imprisoned a Star Spirit. In the Toy Box, several varieties of the Shy Guys are found, including red, blue, yellow, and green Shy Guys, as well as Medi Guys, Pyro Guys, Balloon Guys, Camo Guys, the Gourmet Guy, and the Anti Guy. General Guy hid in a tank and sent his minions after Mario: a group of 15 Shy Guys, 2 Shy Stacks (4 Shy Guys standing on top of each other), and 2 Stilt Guys. The party member Watt played an essential role in defeating General Guy. In Paper Mario: The Thousand-Year Door, Shy Guys play more of a helpful...or neutral role towards Mario. They will sometimes sit in the audience and help Mario or his opponent in battle by messing with the stage. In this sequel, the only enemy Shy Guys are Bandits, Big Bandits, and Badge Bandits. As their names imply, they will steal things from you - the Bandits steal coins, the Big Bandits steal items, and the Badge Bandits steal badges (naturally).