Also, when you put on any of the clothing items from the Hero set (Link's outfit), it makes the sound of discovering a secret in Legend of Zelda games, I love that.
My friend sold me K.K.'s pic, but yeah it's cool. You can also get the Resetti brothers' pics, but I don't remember if there are any NPCs besides Resetti and K.K. you get.
The pumpkin heads also make sounds when you put them on.