Hideaway

Hideaway is a keyword ability created by Aaron Forsythe that gives special access to a card from the library when linked with a second ability. It was featured in Lorwyn, but only on a small number of cards.

Description
A permanent with hideaway enters the battlefield tapped. At that time you may look at the top four cards of your library, exile one face down, then put the rest on the bottom of your library. Usually, a second ability on each card interacts with the exiled card when certain conditions are met, either by allowing it to be cast nearly for free, or simply by putting it into the owner's hand.

History
In Lorwyn, hideaway appeared on a horizontal cycle of rare lands.

Modern Horizons featured the keyword on a creature for the first time.

Rulings

 * When a permanent with hideaway enters the battlefield under your control, you must look at the top four cards of your library and you must exile one of them. If there are fewer than four cards in your library, you look at all of them and (unless your library has no cards in it at all) exile one.
 * The exiled card can be looked at by the player who currently controls the hideaway permanent, as well as by any player who previously controlled that permanent.
 * Each Lorwyn land with hideaway also has an activated ability that allows you to play the exiled card if certain conditions are met. This ability refers only to the card exiled with the hideaway ability.
 * The land's last ability allows you to play the exiled card as part of the resolution of that ability. Timing restrictions based on the card's type are ignored (for instance, if it's a creature or sorcery). Other play restrictions are not (such as "Play [this card] only during combat").
 * If the exiled card is a land, you may play it as a result of the last ability only if it's your turn and you haven't already played a land that turn. This counts as your land play for the turn.
 * If you are unable to play the exiled card due to these or other restrictions (such as having no legal targets for a spell), nothing happens when the land's activated ability resolves, and the card remains exiled face down. You can try to play it later by activating the ability again.
 * If you play a card "without paying its mana cost" (as the last ability says), you can't pay any alternative costs (such as those from evoke or morph). On the other hand, if the card has additional costs, you may pay those.
 * The controller of that ability is the player who gains access to the exiled card. It doesn't matter who owns the exiled card or who exiled it.
 * If you play the land's activated ability and an effect causes you to lose control of the land in response, you can still play the exiled card as the ability resolves.
 * If the card exiled with hideaway has been played or has otherwise left the exile zone, playing the hideaway land's last ability will have no effect.

Trivia

 * During design, Hideaway was a simpler mechanic named "Treasure", and stretched all the way down to common.
 * Hideaway was keyworded because the rules text wouldn't have fit on the card if it wasn't. Watcher for Tomorrow plays into this space, with the vestigial text of "this permanent enters the battlefield tapped" reading as an arbitrary downside.