Hello! When a card says to discard a card (either from your hand or deck) it goes into your discard pile. If it just says to reveal then it will return to where it was revealed from.
So with X ray vision for example the card revealed will stay on top of its owner's deck, but with Starro the card will be put in the discard pile.
So with X ray vision for example the card revealed will stay on top of its owner's deck, but with Starro the card will be put in the discard pile.