Just take a look at Yoshi's Island DS's museum thing, so many of the enemies in the game are Shy Guys. They're like the Goombas/Koopas(though they do appear) or the Kremlins.
I know, I'm just saying they're a constant throughout all the Yoshi games and have many variations, making them the typical enemies of the series.
Regardless though, Shy Guys are the best.