Can't acquire the Ante cards. They are considered still "in the game" as are cards in the library and the graveyard.

If you fail to find something, you still lose half your life, rounded up.

Can't acquire cards that are phased out.

You can't acquire exiled cards because those cards are still in one of the game's zones.

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.