15 Jun 2010
If the targeted creature’s owner has one or more cards in their library, that creature is put into that library directly under the top card.
15 Jun 2010
If the targeted creature is an illegal target by the time Oust resolves, the spell doesn’t resolve. No one gains life.
15 Jun 2010
Note that the creature’s controller, not its owner, is the one who gains life.
15 Jun 2010
If the targeted creature is a token, it will cease to exist after it’s put into its owner’s library.
15 Jun 2010
If the targeted creature’s owner has no cards left in their library, that creature is put into that library as the only card there.