There have only been a few instances where a Shy Guy has been seen without its mask on. In Luigi's Mansion,you suck off Shy Guy Ghost masks and you will see pitch black with 2 skinny oval shaped yellow eyes as long as the shy guy mask eyes that are slightly tilted towards each other,though living Shy guy eyes are likely black,seeing how there was no black in the mask holes when his mask falls off in Mario Power Tennis during Shy Guy's victory.Also,after his mask falls off,you will see a nose if you look closely before it cuts to Luigi looking down at the mask.Seeing how there is no toungue or teeth ever seen in the mouth holes,it is possible that Shy Guys don't have mouthes.