A Shy Guy is an enemy who tries to stop Mario in his quests in the Super Mario series. Shy Guys usually work for the Koopa Troop (mainly in titles like Paper Mario and other games like that), but they don't make so much appearances like the standard Koopa Troopas and Goombas. Maybe because their shy... as a matter of fact, Shy Guys make more entries as friendly shop keepers in Mario Party 8 or minor, cameo roles in games like a ref in Mario & Sonic at the Olympic Games.
Crazee Dayzees behave like Shy Guys, but if Yoshi eats a Crazee Dayzee, it survives when it is swallowed.
Near the end of the track, pretty much the section immediately before the last right turn, a bunch of snowboarding Shy Guys (different colors) surf the snowy slopes constantly. Due to deep snow, the half-pipes rimming the edges are advised in order to dodge these Shy Guys. If you hit them, you will slow down. The only problem is that going on the half pipe slows you down a little, so take the risk if you want. It may or may not be worth it.
Sailing on a far away boat, pirate-style Shy Guys can be seen in the background of GBA Shy Guy Beach. They fire cannonballs that explode like a Bob-omb, just like they did on the original Mario Kart: Super Circuit version (but their cannonballs didn't blow up, which was really a lot less stressful).
Finally, along the railing of a certain part of track on Moonview Highway, the Shy Guy emblem can be seen repeatedly on it... Nothing too special.