Shuffle your library, then reveal the top card. If it's a nonland card, you may cast it without paying its mana cost. If it's a land card, you may put it onto the battlefield and return Unexpected Results to its owner's hand.
1/24/2013 If you reveal a nonland card, you may cast it during the resolution of Unexpected Results. Ignore timing restrictions based on the card’s type. Other timing restrictions, such as “Cast [this card] only during combat,” must be followed.
1/24/2013 If you can’t cast the card (perhaps because there are no legal targets), or if you choose not to, the card will remain on top of the library.
1/24/2013 If you cast a spell “without paying its mana cost,” you can’t pay alternative costs such as overload costs. You can pay additional costs such as kicker costs. If the card has mandatory additional costs, you must pay those.
1/24/2013 If the card has in its mana cost, you must choose 0 as its value.
1/24/2013 If you reveal a land card, Unexpected Results will be returned to your hand only if you put that land card onto the battlefield. If you don’t, Unexpected Results will be put into its owner’s graveyard.
1/24/2013 If you reveal a land card and put that card onto the battlefield, Unexpected Results will be put into its owner’s hand directly from the stack. It won’t be put into any graveyard.