Two big Syno Eupterus that just stay in the rocks all the time and one of my 2 big Clown loaches hasn't been out and about since I moved them all into their new tank!
My wife is always complaining about the fish I bring home that do nothing but hide in caves. They are: Reticulated Hillstream Loach (He actually comes out once in a while), Blue Phantom Pleco, Chocolate Pleco, and my Turushuki. The Glass Cats are pretty shy, too.
my ARTC see him only during water changes and i deliberately move his hiding place so that i can see him well
then there are my synos,corys,minnows,............ in the pond