When Tidehollow Sculler enters the battlefield, target opponent reveals their hand and you choose a nonland card from it. Exile that card.
When Tidehollow Sculler leaves the battlefield, return the exiled card to its owner's hand.
6/7/2013 If Tidehollow Sculler leaves the battlefield before its first ability has resolved, its second ability will trigger. This ability will do nothing when it resolves. Then its first ability will resolve and exile the chosen card forever.