In the upcoming set 'War of the Spark' there is the Planeswalker Karn, the Great Creator. His -2 ability reads as:
-2: You may choose an artifact card you own from outside the game or in exile, reveal that card and add it to your hand
Now my question is, in a sealed tournament, like the Prerelease, is a player allowed to also choose cards from outside his sealed cardpool, or only out of the cards therein. Does anyone know any rulings on stuff like that?
It's the same wording as used on e.g. the Wish cycle from Judgment. An example is Golden Wish. Its rulings at the bottom say
10/1/2009 In a sanctioned event, a card that’s “outside the game” is one that’s in your sideboard. In an unsanctioned event, you may choose any card from your collection.
So in a Sealed event, you're limited to your sideboard, which according to the Tournament Rules are the 'rest' of the opened cards you're not using in your deck. (Of course, exiled cards can be chosen as well.)
7.1 Deck Construction Restrictions
Limited decks must contain a minimum of forty cards. There is no maximum deck size. Any drafted or opened cards not used in a player’s Limited deck function as their sideboard.
