Explore

Explore is a keyword action introduced in Ixalan. It also appeared in Rivals of Ixalan. The mechanic was created by Ken Nagle.

Description
If a creature you control explores, you reveal the top card of your library. If the revealed card is a land, representing your creature finding some new territory you can check out, put that card into your hand. If it's not a land card, your creature comes back empty-handed but still benefits from the attempt. Specifically, you put a +1/+1 counter on it. Then, you decide whether the nonland card goes back on top of your library or into your graveyard. In a sense, Explore is an upgraded version of Scry (though the later released Surveil is actually closer than Scry).

Most creatures that explore, do so because of an triggered ability when they enter the battlefield. Creatures may also explore as a result of an activated ability.

Ixalan has a few cards with abilities that trigger whenever a creature you control explores.

Rulings

 * Once an ability that causes a creature to explore begins to resolve, no player may take any other actions until it's done. Notably, opponents can't try to remove the exploring creature after you reveal a nonland card but before it receives a counter.
 * If no card is revealed, most likely because that player's library is empty, the exploring creature receives a +1/+1 counter.
 * If a resolving spell or ability instructs a specific creature to explore but that creature has left the battlefield, the creature still explores. If you reveal a nonland card this way, you won't put a +1/+1 counter on anything, but you may put the revealed card into your graveyard. Effects that trigger "whenever a creature you control explores" trigger if appropriate.
 * Creatures can't explore unless an effect allows it to do so.
 * When a triggered or an activated ability resolves, if the creature is no longer on the battlefield, it can still explore. If you reveal a land card, you'll still put it into your hand. If you reveal a nonland card, you won't put a +1/+1 counter on the now-absent creature, but you will decide whether the card goes back on your library or into the graveyard.